Sepsis frequently results in acute kidney injury (AKI). Although AKI markedly contributes to mortality in sepsis, its diagnosis is frequently delayed due to limitations of current biomarkers of renal impairment. Neutrophil-gelatinase-associated lipocalin (NGAL) has been demonstrated to be a biomarker of early AKI. This review analyses the potential use of NGAL in sepsis.
by Dr W. Huber, Dr B. Saugel, Dr R. M Schmid and Dr A. Wacker-Gussmann
Pathophysiology, definition and epidemiology of sepsis
Sepsis is a clinical syndrome characterised by systemic inflammatory response to infection [1-2]. Incidence of sepsis has increased by a factor of four within the last three decades, with an estimated incidence of 650,000 cases per year in the USA. SIRS (systemic inflammatory response syndrome) describes a similar inflammatory reaction to non-infectious aetiologies such as poly-trauma, acute pancreatitis and burns. Apart from different aetiology, sepsis and SIRS share a common definition requiring two or more of four criteria of systemic inflammation (fever/hypothermia, tachycardia >90/min, tachypnoe >20/min or paCO2<32mmHg and leukocytosis (>12G/L) or leukopenia (<4G/L) [Table 1], [1-2].
Pathophysiology of sepsis is mainly attributed to imbalanced and generalised release of pro-inflammatory mediators resulting in impaired circulation, tissue injury and organ failures up to multiple-organ-dysfunction-syndrome (MODS). Despite strong evidence for therapeutic efficacy of early causative therapy (treatment of infection source), antibiotics and several supportive strategies, mortality from severe sepsis and septic shock remained up to 20-50% in recent sepsis trials [1-2]. There is an ongoing debate on the benefits of supportive strategies such as hydrocortisone, intensified-insulin-therapy and immunomodulation. However, there is strong consensus about the paramount importance of early sensitive diagnosis and staging of sepsis (severe sepsis and septic shock) in order to initiate appropriate monitoring and therapy as early as possible. In general, patients with severe sepsis will require intensive care and haemodynamic monitoring to optimise circulation.
Diagnoses of severe sepsis and septic shock are mainly based on the evidence of organ failure and emphasize the impact of circulatory failure. The impact of different organ failures on outcome of ICU-patients is substantiated by numerous studies [1-5)]. Interestingly, renal and liver failure were among the organ failures with the most pronounced impact on outcome in several studies [3-5]. At first glance, this might be surprising. However, circulatory and respiratory failure can be easily detected at early stages of severe sepsis, and symptomatic therapy of these organ failures is the main target of intensive care. By contrast, renal and liver failure remain underrated and 'late-stage-diagnosed losses of organ function' in the development of MODS. Difficulties in early detection of renal and hepatic failure by traditional markers has probably also resulted in their under-representation in scoring-systems:
Regarding renal failure, APACHE-II and the SOFA-score are mainly based on absolute serum creatinine values. However, the use of serum creatinine as a marker in these scores and particularly as an early marker of septic renal failure is limited by a number of drawbacks: serum levels of creatinine are dependent on age, gender, muscle mass and race. Furthermore, in case of impaired glomerular filtration, serum creatinine levels can be lowered by tubular secretion, which contributes to the phenomenon of the 'creatinine-blind-range' of renal failure: glomerular-filtration rate (GFR) can decrease to about 50% with serum creatinine levels staying within the normal range. Numerous formulae for GFR estimation slightly improve this drawback. However, GFR formulae are neither part of sepsis definitions nor are they included in SAPS-II, SOFA- and APACHE-II-score. Even the more recent Acute-Kidney-Injury-Network (AKIN) definition of AKI rejected GFR, which has been included in the previous RIFLE-classification (RIFLE: Risk, Injury, Failure; Loss, End-Stage Renal Disease). RIFLE and AKIN as well as the new KDIGO-definition (KDIGO: Kidney Disease: Improving Global Outcomes) are mainly based on changes in serum creatinine compared to baseline values, which are 'known or presumed to have occurred within the prior seven days' [6]. Comparison with a baseline value which is not known in a substantial percentage of patients remains a major problem of these definitions. In general, their usefulness is substantiated as consensus definitions for acute changes in renal function within 2-7 days after the first measurement of serum creatinine rather than being highly sensitive for early AKI. This also relates to the fact that increased serum creatinine on ICU admission of a septic patient might result from constant chronic renal impairment as well as acute renal failure in a patient with previously normal renal function. Both, acute and chronic renal impairment have been demonstrated to significantly influence outcome, albeit to a different degree, with patients with AKI more frequently requiring mechanical ventilation [4, 7].
In the context of sepsis, specification of renal impairment is particularly important: acute septic renal impairment results in markedly worse prognosis, classification as severe sepsis and intensified monitoring in an ICU. By contrast, stable chronic renal impairment in a patients just fulfilling two of the four sepsis criteria would be a minor risk factor contributing to outcome similar to older age. Being a marker of function rather than of injury remains the major drawback of serum creatinine for differentiation of renal impairment.
Approaches to early detection of AKI
Systematic efforts have therefore been made to characterise markers of early renal injury. Using several established animal models of acute renal injury (e.g. ischaemia, nephrotoxic medication including contrast-medium), up-regulation of a number of potential genes has been demonstrated as a short-term reaction to experimental acute renal injury [8]. Among those up-regulated genes and a number of other biomarkers, NGAL, Kidney-Injury-Molecule-1 (KIM-1), interleukin-18 (IL-18) and cystatin C have been most intensively studied. Cystatin C provides characteristics most similar to creatinine: this marker is a cysteine proteinase inhibitor synthesised in all nucleated cells and freely filtered by the glomerulus. The major adavantages over serum creatinine are that cystatin C is not secreted by the tubulus and that it is not affected by age, gender, muscle mass and race. However, with increased levels of cystatin C resulting from accumulation due to decreased glomerular filtration, cystatin C remains as a marker of decrease in renal function rather than a biomarker of early kidney injury. Several studies suggest its slightly earlier (within 24h?) detection of AKI compared to serum creatinine.
Another ‘candidate molecule’ for early detection of AKI is IL-18, a pro-inflammatory cytokine that is induced in the proximal tubule and detected in urine after AKI. In clinical settings, increase in urinary levels within 6h and peak-values within 12h have been demonstrated in cardiopulmonary bypass patients with AKI after 48h according to serum creatinine.
KIM-1 is a transmembrane protein that is markedly over-expressed in the proximal tubule after ischaemic or toxic AKI. A number of clinical studies suggest earlier detection of AKI by KIM-1 compared to serum creatinine, e.g. with elevated urinary KIM-1 levels 12h after paediatric cardiac surgery and prediction of renal replacement therapy (RRT) and mortality in AKI.
NGAL
The most promising biomarker for early acute kidney injury at present is NGAL, which is the profuct of one of seven genes markedly up-regulated in a ischaemia-reperfusion mouse model [8]. NGAL is a 178 amino-acids polypeptide expressed by neutrophils and other epithelial cells including the proximal tubule. NGAL provides several physiological functions including bacteriostatic (depriving bacteria of iron essential for growth), antioxidant (stops free and reactive iron from producing oxygen free radicals) and growth-factor properties (regulates cell proliferation, apoptosis, differentiation). Furthermore, there is a possible rescue role in other epithelia (breast, uterus), and NGAL also is overexpressed in some epithelial tumours.
Regarding its potential clinical use, NGAL has been validated as an early biomarker of AKI induced by cisplatin, contrast-media and cardiac surgery as well as a screening marker for patients at risk in the emergency department (ED) and ICU. In these settings, urinary and plasma levels of NGAL after 2h-12h were significant predictors of AKI defined by later increases in serum creatinine within 24-48h. Depending on setting and methodology, best predictive capabilities of NGAL were found for cut-off values between 50 and 150 µg/L. In a large ED study in 635 patients, urinary NGAL levels clearly differentiated between acute (markedly elevated NGAL) and chronic (not elevated NGAL) renal impairment, whereas there was substantial overlap of serum creatinine values for both groups ([9].
These abilities to discriminate between acute and chronic renal impairment might be particularly useful in patients with sepsis [Figures 1 and 2]. With assessment of renal function in ICU patients based on serum creatinine, normal creatinine levels might be ‘false negative’ and will increase as late as after 48h. On the other hand, increased values of creatinine can result from stable chronic renal impairment. Misinterpretation of these values – ‘false positive’ for septic renal failure – might result in inappropriate allocation of resources, e.g. efficacy for most of the supportive measures in sepsis has been demonstrated predominantly for patients at high risk and with severe sepsis, whereas side effects might outweigh the benefits in patients with less pronounced sepsis.
A potential role for NGAL in sepsis has been suggested in several clinical studies. In 143 paediatric ICU patients Wheeler et al. demonstrated that septic shock, but not SIRS, resulted in a significant elevation of NGAL compared to controls [10]. Furthermore, NGAL on admission was significantly higher in children developing AKI within seven days after admission compared to children without AKI. Serum levels of NGAL and creatinine did not correlate on day one after admission.
A study in 971 ICU patients investigated the predictive capabilities of nine biomarkers on admission regarding severe sepsis within 72h. The best predictive capabilities were found for NGAL, whereas D-dimer, BNP and CRP were of limited use. A score based on NGAL, IL-1-receptor-antagonist and protein C levels significantly distinguished four groups of patients developing no sepsis, severe sepsis, septic shock and death [11]: the area under the curve for the score derived from these three biomarkers was 0.80 for severe sepsis, 0.77 for septic shock and 0.79 for death.
Another recent study found significantly elevated plasma NGAL levels within
4 hours after admission in septic as well as non-septic-patients with AKI according to RIFLE-criteria compared to patients without AKI [12]. Increases in NGAL were even more pronounced in septic compared to non-septic AKI patients. Similarly, urinary NGAL-levels were higher in septic compared to non-septic patients without AKI [13], suggesting that cut-off-values for NGAL to predict AKI might be higher than for non-septic patients.
In summary, clinical applications of NGAL in sepsis comprise early detection of AKI in patients with normal serum creatinine (NGAL+, crea-) compared to patients without renal impairment (NGAL-, crea-). Furthermore, NGAL might be useful to distinguish patients with stable chronic renal impairment (NGAL-, crea+) from patients with ongoing or ‘acute on chronic’ renal injury (NGAL+, crea+) [Figure 1].
With regard to sepsis, more sensitive detection of AKI (NGAL+, crea-) would result in staging as ‘severe sepsis’ instead of sepsis in patients without other organ failures [Figure 2]. Early detection of AKI might help to allocate additional causative (antimicrobial therapy, intervention) and supportive measures for sepsis as well as specific measures to prevent further renal damage. These attempts include intensified haemodynamic monitoring to optimise fluid load, avoidance of further nephrotoxic medications and procedures (contrast-application) or at least prophylactic approaches such as hydration or administration of theophylline or acetylcysteine [13]. Allocation of these resources according to significant predictors and avoidance of further renal impairment carries a high potential for cost effectiveness as emphasised by a number of studies.
Further studies are required to validate that early determination of NGAL improves diagnosis and outcome in septic and non-septic patients at risk of AKI. Future studies should also investigate if including NGAL into scoring (APACHE-II, SOFA, SAPS-II) systems improves their predictive capabilities.
References
1. Dellinger RP et al. Crit Care Med 2008; [published correction appears in Crit Care Med 2008; 36:1394-1396] 36:296-327.
2. German Sepsis Society. German Interdisciplinary Association of Intensive Care and Emergency Medicine. Prevention, diagnosis, therapy and follow-up care of sepsis: 1st revision of S-2k guidelines of the German Sepsis Society (Deutsche Sepsis-Gesellschaft e.V. (DSG)) and the German Interdisciplinary Association of Intensive Care and Emergency Medicine (Deutsche Interdisziplinäre Vereinigung für Intensiv- und Notfallmedizin (DIVI)). Ger Med Sci. 2010 Jun 28;8:Doc14.
3. Chertow GM et al. J Am Soc Nephrol 2005 Nov;16(11):3365-70.
4. Metnitz PG et al. Crit Care Med 2002 Sep;30(9):2051-8.
5. Kramer L et al. Crit Care Med 2007 Apr;35(4):1099-104.
6. KDIGO Clinical Practice Guideline Acute Kidney Injury. Kidney International Supplements 2012; 2: 1-138.
7. Walcher A et al. Ren Fail 2011;33(10):935-42.
8. Mishra J et al. J Am Soc Nephrol 2003 Oct;14(10):2534-43.
9. Nickolas TL et al. Ann Intern Med 2008 Jun 3;148(11):810-9.
10. Wheeler DS et al. Crit Care Med 2008 Apr;36(4):1297-303.
11. Shapiro NI et al. Ann Emerg Med 2010 Jul;56(1):52-59.e1.
12. Lentini P et al. Crit Care Res Pract 2012: 2012:856401. Epub 2012 Feb 14.
13. De Geus HR et al. Am J Respir Crit Care Med 2011 Apr 1;183(7):907-14. Epub 2010 Oct 8
14. Huber W et al. Radiology 2006; 239(3):793-804.
The authors
Wolfgang Huber MD, Bernd Saugel MD, Roland M Schmid MD
II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar der Technischen Universität München, Ismaningerstr. 22, D-81675 München, Germany
and
Annette Wacker-Gussmann MD
Universitätsklinik Tübingen, Kinderheilkunde und Jugendmedizin, Abteilung für Neonatologie, Calwerstr. 7, D72076 Tübingen, Germany
Correspondence to Wolfgang Huber
e-mail: wolfgang.huber@lrz.tu-muenchen.de; Tel: +0049 (0) 89 4140-5478
Early detection of acute kidney injury in sepsis: how about NGAL?
, /in Featured Articles /by 3wmediaSepsis frequently results in acute kidney injury (AKI). Although AKI markedly contributes to mortality in sepsis, its diagnosis is frequently delayed due to limitations of current biomarkers of renal impairment. Neutrophil-gelatinase-associated lipocalin (NGAL) has been demonstrated to be a biomarker of early AKI. This review analyses the potential use of NGAL in sepsis.
by Dr W. Huber, Dr B. Saugel, Dr R. M Schmid and Dr A. Wacker-Gussmann
Pathophysiology, definition and epidemiology of sepsis
Sepsis is a clinical syndrome characterised by systemic inflammatory response to infection [1-2]. Incidence of sepsis has increased by a factor of four within the last three decades, with an estimated incidence of 650,000 cases per year in the USA. SIRS (systemic inflammatory response syndrome) describes a similar inflammatory reaction to non-infectious aetiologies such as poly-trauma, acute pancreatitis and burns. Apart from different aetiology, sepsis and SIRS share a common definition requiring two or more of four criteria of systemic inflammation (fever/hypothermia, tachycardia >90/min, tachypnoe >20/min or paCO2<32mmHg and leukocytosis (>12G/L) or leukopenia (<4G/L) [Table 1], [1-2]. Pathophysiology of sepsis is mainly attributed to imbalanced and generalised release of pro-inflammatory mediators resulting in impaired circulation, tissue injury and organ failures up to multiple-organ-dysfunction-syndrome (MODS). Despite strong evidence for therapeutic efficacy of early causative therapy (treatment of infection source), antibiotics and several supportive strategies, mortality from severe sepsis and septic shock remained up to 20-50% in recent sepsis trials [1-2]. There is an ongoing debate on the benefits of supportive strategies such as hydrocortisone, intensified-insulin-therapy and immunomodulation. However, there is strong consensus about the paramount importance of early sensitive diagnosis and staging of sepsis (severe sepsis and septic shock) in order to initiate appropriate monitoring and therapy as early as possible. In general, patients with severe sepsis will require intensive care and haemodynamic monitoring to optimise circulation. Diagnoses of severe sepsis and septic shock are mainly based on the evidence of organ failure and emphasize the impact of circulatory failure. The impact of different organ failures on outcome of ICU-patients is substantiated by numerous studies [1-5)]. Interestingly, renal and liver failure were among the organ failures with the most pronounced impact on outcome in several studies [3-5]. At first glance, this might be surprising. However, circulatory and respiratory failure can be easily detected at early stages of severe sepsis, and symptomatic therapy of these organ failures is the main target of intensive care. By contrast, renal and liver failure remain underrated and 'late-stage-diagnosed losses of organ function' in the development of MODS. Difficulties in early detection of renal and hepatic failure by traditional markers has probably also resulted in their under-representation in scoring-systems: Regarding renal failure, APACHE-II and the SOFA-score are mainly based on absolute serum creatinine values. However, the use of serum creatinine as a marker in these scores and particularly as an early marker of septic renal failure is limited by a number of drawbacks: serum levels of creatinine are dependent on age, gender, muscle mass and race. Furthermore, in case of impaired glomerular filtration, serum creatinine levels can be lowered by tubular secretion, which contributes to the phenomenon of the 'creatinine-blind-range' of renal failure: glomerular-filtration rate (GFR) can decrease to about 50% with serum creatinine levels staying within the normal range. Numerous formulae for GFR estimation slightly improve this drawback. However, GFR formulae are neither part of sepsis definitions nor are they included in SAPS-II, SOFA- and APACHE-II-score. Even the more recent Acute-Kidney-Injury-Network (AKIN) definition of AKI rejected GFR, which has been included in the previous RIFLE-classification (RIFLE: Risk, Injury, Failure; Loss, End-Stage Renal Disease). RIFLE and AKIN as well as the new KDIGO-definition (KDIGO: Kidney Disease: Improving Global Outcomes) are mainly based on changes in serum creatinine compared to baseline values, which are 'known or presumed to have occurred within the prior seven days' [6]. Comparison with a baseline value which is not known in a substantial percentage of patients remains a major problem of these definitions. In general, their usefulness is substantiated as consensus definitions for acute changes in renal function within 2-7 days after the first measurement of serum creatinine rather than being highly sensitive for early AKI. This also relates to the fact that increased serum creatinine on ICU admission of a septic patient might result from constant chronic renal impairment as well as acute renal failure in a patient with previously normal renal function. Both, acute and chronic renal impairment have been demonstrated to significantly influence outcome, albeit to a different degree, with patients with AKI more frequently requiring mechanical ventilation [4, 7]. In the context of sepsis, specification of renal impairment is particularly important: acute septic renal impairment results in markedly worse prognosis, classification as severe sepsis and intensified monitoring in an ICU. By contrast, stable chronic renal impairment in a patients just fulfilling two of the four sepsis criteria would be a minor risk factor contributing to outcome similar to older age. Being a marker of function rather than of injury remains the major drawback of serum creatinine for differentiation of renal impairment. Approaches to early detection of AKI
Systematic efforts have therefore been made to characterise markers of early renal injury. Using several established animal models of acute renal injury (e.g. ischaemia, nephrotoxic medication including contrast-medium), up-regulation of a number of potential genes has been demonstrated as a short-term reaction to experimental acute renal injury [8]. Among those up-regulated genes and a number of other biomarkers, NGAL, Kidney-Injury-Molecule-1 (KIM-1), interleukin-18 (IL-18) and cystatin C have been most intensively studied. Cystatin C provides characteristics most similar to creatinine: this marker is a cysteine proteinase inhibitor synthesised in all nucleated cells and freely filtered by the glomerulus. The major adavantages over serum creatinine are that cystatin C is not secreted by the tubulus and that it is not affected by age, gender, muscle mass and race. However, with increased levels of cystatin C resulting from accumulation due to decreased glomerular filtration, cystatin C remains as a marker of decrease in renal function rather than a biomarker of early kidney injury. Several studies suggest its slightly earlier (within 24h?) detection of AKI compared to serum creatinine.
Another ‘candidate molecule’ for early detection of AKI is IL-18, a pro-inflammatory cytokine that is induced in the proximal tubule and detected in urine after AKI. In clinical settings, increase in urinary levels within 6h and peak-values within 12h have been demonstrated in cardiopulmonary bypass patients with AKI after 48h according to serum creatinine.
KIM-1 is a transmembrane protein that is markedly over-expressed in the proximal tubule after ischaemic or toxic AKI. A number of clinical studies suggest earlier detection of AKI by KIM-1 compared to serum creatinine, e.g. with elevated urinary KIM-1 levels 12h after paediatric cardiac surgery and prediction of renal replacement therapy (RRT) and mortality in AKI.
NGAL
The most promising biomarker for early acute kidney injury at present is NGAL, which is the profuct of one of seven genes markedly up-regulated in a ischaemia-reperfusion mouse model [8]. NGAL is a 178 amino-acids polypeptide expressed by neutrophils and other epithelial cells including the proximal tubule. NGAL provides several physiological functions including bacteriostatic (depriving bacteria of iron essential for growth), antioxidant (stops free and reactive iron from producing oxygen free radicals) and growth-factor properties (regulates cell proliferation, apoptosis, differentiation). Furthermore, there is a possible rescue role in other epithelia (breast, uterus), and NGAL also is overexpressed in some epithelial tumours.
Regarding its potential clinical use, NGAL has been validated as an early biomarker of AKI induced by cisplatin, contrast-media and cardiac surgery as well as a screening marker for patients at risk in the emergency department (ED) and ICU. In these settings, urinary and plasma levels of NGAL after 2h-12h were significant predictors of AKI defined by later increases in serum creatinine within 24-48h. Depending on setting and methodology, best predictive capabilities of NGAL were found for cut-off values between 50 and 150 µg/L. In a large ED study in 635 patients, urinary NGAL levels clearly differentiated between acute (markedly elevated NGAL) and chronic (not elevated NGAL) renal impairment, whereas there was substantial overlap of serum creatinine values for both groups ([9].
These abilities to discriminate between acute and chronic renal impairment might be particularly useful in patients with sepsis [Figures 1 and 2]. With assessment of renal function in ICU patients based on serum creatinine, normal creatinine levels might be ‘false negative’ and will increase as late as after 48h. On the other hand, increased values of creatinine can result from stable chronic renal impairment. Misinterpretation of these values – ‘false positive’ for septic renal failure – might result in inappropriate allocation of resources, e.g. efficacy for most of the supportive measures in sepsis has been demonstrated predominantly for patients at high risk and with severe sepsis, whereas side effects might outweigh the benefits in patients with less pronounced sepsis.
A potential role for NGAL in sepsis has been suggested in several clinical studies. In 143 paediatric ICU patients Wheeler et al. demonstrated that septic shock, but not SIRS, resulted in a significant elevation of NGAL compared to controls [10]. Furthermore, NGAL on admission was significantly higher in children developing AKI within seven days after admission compared to children without AKI. Serum levels of NGAL and creatinine did not correlate on day one after admission.
A study in 971 ICU patients investigated the predictive capabilities of nine biomarkers on admission regarding severe sepsis within 72h. The best predictive capabilities were found for NGAL, whereas D-dimer, BNP and CRP were of limited use. A score based on NGAL, IL-1-receptor-antagonist and protein C levels significantly distinguished four groups of patients developing no sepsis, severe sepsis, septic shock and death [11]: the area under the curve for the score derived from these three biomarkers was 0.80 for severe sepsis, 0.77 for septic shock and 0.79 for death.
Another recent study found significantly elevated plasma NGAL levels within
4 hours after admission in septic as well as non-septic-patients with AKI according to RIFLE-criteria compared to patients without AKI [12]. Increases in NGAL were even more pronounced in septic compared to non-septic AKI patients. Similarly, urinary NGAL-levels were higher in septic compared to non-septic patients without AKI [13], suggesting that cut-off-values for NGAL to predict AKI might be higher than for non-septic patients.
In summary, clinical applications of NGAL in sepsis comprise early detection of AKI in patients with normal serum creatinine (NGAL+, crea-) compared to patients without renal impairment (NGAL-, crea-). Furthermore, NGAL might be useful to distinguish patients with stable chronic renal impairment (NGAL-, crea+) from patients with ongoing or ‘acute on chronic’ renal injury (NGAL+, crea+) [Figure 1].
With regard to sepsis, more sensitive detection of AKI (NGAL+, crea-) would result in staging as ‘severe sepsis’ instead of sepsis in patients without other organ failures [Figure 2]. Early detection of AKI might help to allocate additional causative (antimicrobial therapy, intervention) and supportive measures for sepsis as well as specific measures to prevent further renal damage. These attempts include intensified haemodynamic monitoring to optimise fluid load, avoidance of further nephrotoxic medications and procedures (contrast-application) or at least prophylactic approaches such as hydration or administration of theophylline or acetylcysteine [13]. Allocation of these resources according to significant predictors and avoidance of further renal impairment carries a high potential for cost effectiveness as emphasised by a number of studies.
Further studies are required to validate that early determination of NGAL improves diagnosis and outcome in septic and non-septic patients at risk of AKI. Future studies should also investigate if including NGAL into scoring (APACHE-II, SOFA, SAPS-II) systems improves their predictive capabilities.
References
1. Dellinger RP et al. Crit Care Med 2008; [published correction appears in Crit Care Med 2008; 36:1394-1396] 36:296-327.
2. German Sepsis Society. German Interdisciplinary Association of Intensive Care and Emergency Medicine. Prevention, diagnosis, therapy and follow-up care of sepsis: 1st revision of S-2k guidelines of the German Sepsis Society (Deutsche Sepsis-Gesellschaft e.V. (DSG)) and the German Interdisciplinary Association of Intensive Care and Emergency Medicine (Deutsche Interdisziplinäre Vereinigung für Intensiv- und Notfallmedizin (DIVI)). Ger Med Sci. 2010 Jun 28;8:Doc14.
3. Chertow GM et al. J Am Soc Nephrol 2005 Nov;16(11):3365-70.
4. Metnitz PG et al. Crit Care Med 2002 Sep;30(9):2051-8.
5. Kramer L et al. Crit Care Med 2007 Apr;35(4):1099-104.
6. KDIGO Clinical Practice Guideline Acute Kidney Injury. Kidney International Supplements 2012; 2: 1-138.
7. Walcher A et al. Ren Fail 2011;33(10):935-42.
8. Mishra J et al. J Am Soc Nephrol 2003 Oct;14(10):2534-43.
9. Nickolas TL et al. Ann Intern Med 2008 Jun 3;148(11):810-9.
10. Wheeler DS et al. Crit Care Med 2008 Apr;36(4):1297-303.
11. Shapiro NI et al. Ann Emerg Med 2010 Jul;56(1):52-59.e1.
12. Lentini P et al. Crit Care Res Pract 2012: 2012:856401. Epub 2012 Feb 14.
13. De Geus HR et al. Am J Respir Crit Care Med 2011 Apr 1;183(7):907-14. Epub 2010 Oct 8
14. Huber W et al. Radiology 2006; 239(3):793-804.
The authors
Wolfgang Huber MD, Bernd Saugel MD, Roland M Schmid MD
II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar der Technischen Universität München, Ismaningerstr. 22, D-81675 München, Germany
and
Annette Wacker-Gussmann MD
Universitätsklinik Tübingen, Kinderheilkunde und Jugendmedizin, Abteilung für Neonatologie, Calwerstr. 7, D72076 Tübingen, Germany
Correspondence to Wolfgang Huber
e-mail: wolfgang.huber@lrz.tu-muenchen.de; Tel: +0049 (0) 89 4140-5478
Scientific literature review: sepsis
, /in Featured Articles /by 3wmediaThere are a huge number of peer-reviewed papers covering sepsis, and it is frequently difficult for healthcare professionals to keep up with the literature. As a special service to our readers, CLI presents a few key abstracts from the clinical and scientific literature chosen by our editorial board as being particularly worthy of attention.
Predictors of survival in sepsis: what is the best inflammatory marker to measure?
Lichtenstern C et al. Curr Opin Infect Dis. 2012 Jun;25(3):328-36.
Beyond the widely used acute-phase proteins C-reactive protein (CRP) and procalcitonin (PCT) in sepsis manegement, many new molecules have been studied deriving from different organs or cells affected, due to the systemic nature of sepsis. Cytokines, coagulation factors/characteristics, vasoactive hormones and several others have recently proved to be relevant in sepsis syndrome and probably useful for outcome prediction. However, single time point measurements may be less predictive than consideration of the time-dependent course of parameters. Many biomarkers display relevant correlation with the clinical outcome of patients with severe sepsis and septic shock. Consideration of their time courses may be more reliable than absolute levels. Clinical decision should not only be based on biomarkers but organ dysfunctions, for example, should also be taken into account.
Cytokine profiles of preterm neonates with fungal and bacterial sepsis
Sood BG et al. Pediatr Res. 2012 May 4.
Information on cytokine profiles in fungal sepsis (FS), an important cause of mortality in extremely low birthweight infants (ELBW), is lacking. The authors hypothesised that cytokine profiles in the 1st 21 days of life in ELBW with FS differ from those with bacterial sepsis (BS) or no sepsis (NS). In a secondary analyses of the NICHD Cytokine study, three groups were defined – FS (≥1 episode of FS), BS (≥1 episode of BS without FS) and NS. Association between 11 cytokines assayed in dried blood spots obtained on days 0-1, 3±1, 7±2, 14±3, and 21±3 and sepsis group was explored.Of 1066 infants, 89 had FS and 368 had BS. Compared to BS, FS was more likely to be associated with lower birthweight, vaginal delivery, patent ductus arteriosus, postnatal steroids, multiple central lines, longer respiratory support and hospital stay, and higher mortality (p<0.05). Analyses controlling for covariates showed significant group differences over time for IFN-γ, IL-10, IL-18, TGF-β and TNF-α (p<0.05). These differences, which may have implications for diagnosis and treatment, require validation in rigorously designed prospective studies.
Prognostic value of proadrenomedullin in severe sepsis and septic shock patients with community-acquired pneumonia
Suberviola B et al. Prieto B. Swiss Med Wkly. 2012 Mar 19;142:w13542.
Midregional proadrenomedullin (proADM) is a novel biomarker with potential prognostic utility in patients with community-acquired pneumonia. The aim of this study was to investigate the value of proADM levels for severity assessment and outcome prediction in severe sepsis and septic shock due to CAP. The prospective observational study included 49 patients admitted to ICU with both a clinical and radiologic diagnosis of pneumonia and fulfilling criteria for severe sepsis or septic shock. The prognostic accuracy of proADM levels was compared with those of pneumonia severity index and of procalcitonin (PCT) and C-reactive protein (CRP). Forty-nine patients with severe sepsis or septic shock due to CAP were included in the study. Mortality was 24.5% for ICU and 34.7% for hospital mortality. In all cases proADM values at ICU admission were pathological (considering normal proADM levels <4 nmol/L). ProADM consistently rose as PSI class advanced from II to V (p = 0.02). Median proADM levels were higher (p <0.01) in hospital non-survivors 5.0 (1.9-10.1) nmol/L vs. survivors 1.7 (1.3-3.1) nmol/L. These differences were also significant with respect to ICU mortality. The receiver-operating characteristic curve for proADM yielded an AUC of 0.72; better than the AUC for PCT and CRP (0.40 and 0.44 respectively) and similar to PSI (0.74). In this study MR-proADM levels correlated with increasing severity of illness and death. High MR-proADM levels thus offer additional risk stratification in high-risk CAP patients.
Direct thrombin inhibitor assays
, /in Featured Articles /by 3wmediaWe have investigated the effects of three (Lepirudin, Argatroban and Bivalirudin) direct thrombin inhibitors (DTI) on routine and dedicated assays.
We found routine tests to be non-discriminative between concentrations of different DTI. The dedicated Hemoclot assay showed identical lineair increases for all three DTI.
We conclude that a dedicated calibrated assay based on a diluted thrombin time (Hemoclot) appears to be the most suitable assay for monitoring purpose.
by Dr Joyce Curvers, Dr Volkher Scharnhorst and Dr Daan van de Kerkhof
Clinical background
The use of direct thrombin inhibitors (DTIs) for prophylactic or therapeutic anticoagulation is increasing due to their predictable bioavailability, short half life and limited interaction with other medication [1-5]. The current idea is that the newer anticoagulants should not require laboratory monitoring because of these advantages. However, although monitoring of anticoagulant therapy may not be required for ‘standard’ patients, patients with an increased bleeding risk, specific co-medication (such as amiodarone or bridging therapy with coumarins), or a deviant body mass or water homeostasis (e.g. neonates, during pregnancy, the obese, the elderly, in renal insufficiency, oedema, cardiac disease) may still require occasional blood analysis. In addition when the compliance or effectiveness of the anticoagulants is doubted, measurement of the coagulation status can be crucial for the correct treatment of a patient. Since DTIs interfere with the central clotting enzyme thrombin, almost every coagulation assay is affected by its presence in blood. This also accounts for routinely used assays such as the aPTT or PT (and INR) [6].
Up to date, there is no consensus on how oral or intravenous administrable DTI should be monitored and specifically which assay should ideally be used [6,7]. In this study we performed an in vitro study in which we investigated the effect of increasing concentration levels of three DTIs: lepirudin, bivalirudin and argatroban in six plasma pools on aPTT, PT, TT and on dedicated DTI-assays (Hemoclot from Hyphen BioMed and Ecarin Clotting Time from STAGO) on a coagulation analyser (STA-R Evolution, Roche).
Materials and methods
Six different pools (N>20 samples per pool) were collected from residual plasma from patients with aPTT and PT values within reference limits (assuming that patients did not take any anticoagulant medication based on their normal aPTT and PT values).
Argatroban (Arganova, Mitsubishi Pharma, lot PF41977, 100 mg/mL) and lepirudin (Refludan, Pharmion, lot 24661611L, 50mg) were provided by the local hospital pharmacy. Bivalirudin (Angiox or angiomax, The Medicines company, lot 1574697, 250 mg) was a kind gift from the Medicines Company. All DTIs were diluted with saline (0,9% NaCl) to 5 g/L. These stock solutions were spiked into the pooled plasmas (N=6) to reach final concentrations of 1, 2, 3, 4 and 5 mg/L. Therapeutic doses of DTI are currently advised at 2 mg/L (according to package leaflet). Different plasma pools with each different concentration of different DTIs were frozen in triplicates at <-70˚C until time of measurement. Clotting times in the aPTT, prothrombin time (PT) and thrombin time (TT) as well as the dedicated assays Hemoclot (a diluted TT) and the Ecarin Clotting Time (ECT) were recorded. Results
For all thrombin inhibitors investigated here, the fold increase compared to no DTI in six pools measured in routine tests (aPTT, PT and thrombin time) are shown in Figure 1. The aPTT shows a non-linear concentration-response relationship with a more gradual increase at higher DTI concentrations resulting in a limited sensitivity of the assay in this range. The concentration-response relationship for the PT was linear but with different sensitivities for the different DTIs. The low sensitivity was found especially for bivalirudin and lepuridin with respectively a maximum 2- and 3-fold increase in PT coagulation time at 5 mg/L. The thrombin time also showed a linear concentration-response relationship, with a high increase in coagulation time as function of concentration, especially for lepuridin, exceeding the maximum installed measuring range (i.e. 240 sec) of the STA-R evolution.
Figure 2 shows the data for the dedicated thrombin inhibitor tests. Similar results as for the PT were observed for the ECT, also with respect to the differences between different direct thrombin inhibitors. Lepirudin showed an increase in ratio up to 5-fold baseline value in the ECT. The increase in the Hemoclot was linear for all DTIs with similar increase as a function of concentration measured.
Conclusion
Concluding, dedicated DTI assays overcome the drawbacks of routine assays such as the PT, aPTT or TT, in which the ability to discriminate between different concentrations is insufficient. This would suggest that monitoring DTIs using the aPTT is obsolete. We have shown that dose-response curves of DTIs in dedicated assays such as the Hemoclot and ECT are acceptable. Moreover, they can be applied in a routine setting, have short turn around times and can be used to distinguish inappropriate from appropriate dosing without the necessity of reanalysis after dilution. Given that a calibrator is included in the assay kit and the test gives similar result for different DTI formulations, the Hemoclot assay appears to be the most suitable assay for monitoring purposes (apparent in this study). As more new oral thrombin inhibitors such as dabigatran etexilate find their way into troutine practice, dedicated assays may aid the clinician in better decision making concerning anticoagulant therapy, especially in certain groups of patients in need of monitoring. However, research is needed to properly determine therapeutic and prophylactic concentration ranges, with calibrated dedicated DTI assays.
Current status
The administration of (oral and) intravenous direct thrombin inhibitors is increasing, since more applications are becoming available. The pharmaceutical companies pay little attention to the fact that, in certain situations, indication of the concentration is warranted.
We are currently validating a calibrated assay based on a diluted thrombin time for use in our laboratory (and clinic), as are several other laboratories nation-wide.
Future prospects
Up to now little is known about interference of different anticoagulants combined with DTI (e.g. during bridging therapy) and the effects on the different dedicated assays. Future research will show the value of the different DTI assays in monitoring patients in order to distinguish proper dosing from under dosage or over dosage.
Moreover, standardisation and calibration of (present and new) dedicated assays for the measurement of DTI is a major issue of concern. Therefore we are currently conducting research in which a comparison of coagulation assay results with actual concentrations of the different DTI (measured with LCMSMS) is investigated.
Notification
Part of this publication is included in a manuscript that will be published in the American Journal of Clinical Pathology.
References
1. Di Nisio M, Middeldorp S, Buller HR. Direct thrombin inhibitors. N Engl J Med 2005; 353: 1028-1040.
2. Stone GW, Witzenbichler B, Guagliumi G et al. HORIZONS-AMI Trial Investigators. Bivalirudin during primary PCI in acute myocardial infarction. N Engl J Med 2008; 358: 2218-2230.
3. Mehran R, Lansky AJ, Witzenbichler B et al. HORIZONS-AMI Trial Investigators. Bivalirudin in patients undergoing primary angioplasty for acute myocardial infarction (HORIZONS-AMI): 1-year results of a randomised controlled trial. Lancet 2009; 374: 1149-1159.
4. Connolly SJ, Ezekowitz MD, Yusuf S et al. RE-LY steering committee and investigators Dabigatran versus warfarin in patients with atrial fibrillation. N Engl J Med 2009; 361: 1139-1151. Erratum in: N Engl J Med 2010 Nov 4;363(19):1877
5. Schulman S, Kearon C, Kakkar AK et al. for the RE-COVER study group. Dabigatran versus warfarin in the treatment of acute venous thromboembolism. N Engl J Med 2009; 361: 2342-2352.
6. Gosslin RC, Dager WE, King JH et al. Effect of direct thrombin inhibitors, bivalirudin, lepirudin and argatroban, on prothrombin time and INR values. Am J Clin Pathol 2004; 121: 593-599.
7. Van Ryn J, Stangier J, Haertter S et al. Dabigatran etexilate – a novel, reversible, oral direct thrombin inhibitor: interpretation of coagulation assays and reversal of anticoagulant activity. Thromb Haemost 2010; 103: 1116-1127.
The authors
Joyce Curvers PhD, Volkher Scharnhorst PhD and Daan van de Kerkhof PhD
Clinical Laboratory
Catharina Hospital Eindhoven
Eindhoven
The Netherlands
The case for better blood management
, /in Featured Articles /by 3wmediaAlthough significant progress has been made to improve blood safety and efficiency, laboratories still face workforce challenges, and the lack of global standards and better quality controls in blood management and haemovigilance pose a threat to patient safety. To help address these challenges, a symposium was hosted at the 2011 American Association of Blood Banks Annual Meeting with key opinion leaders from the transfusion medicine departments of the Cleveland Clinic, Children’s Hospital Los Angeles and USC Medical Center.
The attending experts broadly agreed that the key to safe, efficient blood management boils down to the ‘5Rs’: ensuring the Right patient gets the Right donor unit at the Right time, the Right way and for the Right reason. Presentations at the symposium discussed how the transfusion laboratory can deliver on the 5Rs through improvements in blood management and haemovigilance practices.
by Scott Saccal
Improving blood safety
Laboratories strive to protect patients’ health and deliver safe blood and blood components to the right person at the right time, but they are under constant pressure to do more with less – including fewer skilled laboratory technicians and scarcer financial resources. To help in meeting these demands, blood bank laboratories are increasingly employing automation. For example, many blood banks are standardising across instrument platforms and implementing testing technologies such as Column Agglutination (CAT). These testing methods are easier to use, and help reduce the opportunity for error and variation among both technologists and tests because they provide stable and clear endpoints that deliver accurate, objective and consistent results.
Automation helps minimise the labor-intensive, time-consuming manual tests that require specialised skills and significant experience to master, such as patient and unit typing, antibody screening and cross-matching. Automation also increases the capacity of technologists so they can focus on priorities such as time-sensitive emergency situations, difficult patient workups and quality-improvement processes. For example, computerised physician order entries have been found to reduce errors related to labour-intensive tasks by 50 percent, and all errors in general by 80 percent [1,2]. Ultimately, automated testing can increase a lab’s capacity, potentially allowing it to serve more patients while helping it operate more efficiently.
New approaches to load management and haemovigilance
Quality controls help ensure the safety of the patient at the end of the bloodline by helping to assure that from the moment a donation is made, the right blood and blood products are delivered to the right patient at the right time, and in the right way for the right reason. While great strides have been made to implement quality controls for the highest level of patient safety, there remains much work to be done.
Across the globe, a total of 106 countries have national guidelines on blood management, yet no universal safety standards exist. Further, broken system links and human errors due to distraction, fatigue and inattention account for approximately 70 percent of lab errors and cause catastrophic consequences such as the inappropriate administration of blood and/or adverse reactions [3]. Giving the wrong donor unit or giving an inappropriate transfusion can lead to serious complications, disease transmission and even fatal haemolytic reactions [4].
To combat the high incidence of laboratory errors, many hospitals and clinics are appointing Transfusion Safety Officers (TSO), to oversee work outside of the laboratory to improve patient safety during transfusions [5]. The increase in demand for blood and blood components suggests that additional measures will be needed to promote transfusion safety across departments, oversee institution-wide haemovigilance and error and accident reporting, provide education on transfusion reactions, implement guidelines, perform safety training and identify new technology for enhanced safety.
Additionally, hospitals and healthcare institutions around the world are developing ways to meet new standards – both by instituting their own rigorous policies, and by understanding and implementing the guidelines from organisations that oversee the safety of transfusions. The UK’s Serious Hazard of Transfusion programme and the U.S. Centers for Disease Control (CDC) National Healthcare Safety Network (NHSN) suggest voluntary reporting structures to create a reliable source of information for the medical and scientific community about blood transfusion issues, including warning facilities about adverse events that could be systemic.
Industry groups also are striving to improve patient care and safety while maximising healthcare system efficiencies. For example, AABB collaborates with the U.S. Department of Health and Human Services on biovigilance activities, including programmes directed at a variety of different domains such as donor haemovigilance and transfusion recipient haemovigilance. Through the collaboration, the organisations are gathering and analysing data to help find trends and establish best practices for safer, more efficient transfusions and transplants [6]. Similarly, the International Society of Blood Transfusion (ISBT) and the European Haemovigilance Network (EHN) began a working group in 2004 focused on creating a common set of definitions for issues in the field, which would enable global benchmarking and is intended ultimately to increase the safety of blood donors and recipients around the world [7].
Shared commitment to patient safety
Protecting the precious life of a patient who will receive a unit of blood remains the focus of blood bankers everywhere. As the pressures and demands rise, labs are finding new ways to be efficient and haemovigilant, while never losing sight of the real person at the end of the bloodline. Despite the continued shortage of highly skilled technologists and scientists entering the laboratory science workforce, blood bankers are utilising automation and best practices to improve transfusion testing, and implementing new approaches to blood management and haemovigilance to deliver on the 5Rs of blood safety. Protecting the safety of patients through efficient blood management and haemovigilance is a commitment all of us share as part of the transfusion medicine community.
References
1. Bates DW et al. Effect of computerized order entry and a team intervention on prevention of serious medication errors. Journal of the American Medical Association 1998; 280: 1211-1212
2. Bates DW et al. The impact of computerized order entry on medication error prevention. Journal of American Medical Informatics Association 1999; 6: 313-332.
3. Kaplan HS. Getting the right blood to the right patient: the contribution of near-miss event reporting and barrier analysis. Transfusion Clinique et Biologique 2005; 2: 380-384.
4. Shulman Ira A. ‘Assuring That The Right Patient Gets The Right Donor Unit, At The Right Time, The Right Way, And For The Right Reason.’ Slide 6. AABB annual meeting. San Diego, CA. Ortho Clinical Diagnostics Blood Management Symposium. October 24, 2011
5. Davey Richard J. ‘The Safety of the Blood Supply.’ Food and Drug Administration Division of Blood Applications webinar. Available at: http://www.fda.gov/downloads/AboutFDA/Transparency/Basics/UCM245738.pdf. Accessed October 20, 2011.
6. Biovigilance – AABB program — http://www.aabb.org/programs/biovigilance/Pages/default.aspx
7. Haemovigilance – ISBT — http://www.isbtweb.org/fileadmin/user_upload/WP_on_Haemovigilance/ISBT_StandardSurveillanceDOCO_2008__3_.pdf
The author
Scott Saccal
Worldwide Marketing Director
Transfusion Medicine
Ortho Clinical Diagnostics
Biomarkers in the management of cardiorenal syndrome
, /in Featured Articles /by 3wmediaThe cardiorenal syndrome (CRS) involves both kidney failure and heart failure, with the failing organ initially being either the heart or the kidney; usually one failing organ leads to the failure of the other. While use of biomarkers and imaging techniques can assess cardiovascular function, the assessment of renal injury and function is complex in CRS patients. This article discusses some of the novel markers for the assessment of renal function and injury.
Renal dysfunction is an independent and significant contributor to poor heart failure outcomes. Serum creatinine (SCr), the most frequently used marker for clinical assessment of renal dysfunction and injury, is at best a retrospective window. Glomerular filtration rate, GFR, considered the best overall measure of renal function (RF), is similarly affected by multiple variables, but novel biomarkers of renal injury and function are now available. These biomarkers also have limitations but they address gaps in the information provided from use of conventional biomarkers
A marker of renal function: cystatin-C
Cystatin C, an endogenous proteinase inhibitor of low molecular weight (13-kDa), possesses many features that make it attractive as a surrogate marker of RF and GFR. It is synthesised and released into plasma by all nucleated cells at a constant rate, is freely filtered by the glomerulus and completely reabsorbed by the proximal tubules. It can be easily measured in the serum and plasma without the need for a urine sample or complex equations. It is not affected by changes in body mass, nutrition, age or gender, making it potentially more beneficial in critically ill patients, elderly and children. It has been validated as a marker of GFR in patients with pre-existing renal dysfunction and acute kidney injury (AKI) as levels increase before SCr. In congestive heart failure (CHF) Cys-C is superior to SCr based estimates, which underestimate GFR. This appears to extend to acure decompensated heart failure (ADHF) admissions without advanced RF. Cys-C also reflects myocardial stress and damage, reflects more advanced left ventricular diastolic and right ventricular systolic dysfunction and is an independent predictor of long-term prognosis after adjusting for myocardial factors. The advantage of Cys-C over SCr appears greater and more conclusive for ruling in renal injury in affected patients. Other benefits include predicting future CV events in intermediate-risk individuals, mainly through the identification of those unlikely to develop events; it is a stronger predictor of adverse events than conventional measurement of RF and, in combination with cardiac troponin T and N-terminal–pro-brain natriuretic peptide, it improves risk stratification for CV mortality (inclusive of HF) beyond models of established risk factors.
Novel assessments of renal injury
The potential to attenuate or reverse renal injury is far less likely when renal dysfunction is already evident, at least based on current assessment methods. Several promising AKI biomarkers arenow available.
Neutrophil gelatinase-associated lipocalin
Human neutrophil gelatinase-associated lipocalin (NGAL) is a 25-kDa protein initially described to be bound to gelatinase in specific granules of the neutrophil, with recent evidence suggesting physiological activity in the kidney. It is expressed and secreted by immune cells, hepatocytes and renal tubular cells in various pathologic states. NGAL exerts bacteriostatic effects, which are explained by its ability to capture and deplete siderophores, small iron-binding molecules that are synthesised by certain bacteria as a means of iron acquisition and role in cell survival, inflammation and matrix degradation. NGAL is up regulated more than 10-fold in post ischaemic renal injury in a mouse model and secreted relatively early into the urine. Several recent studies in homogenous (adult and paediatric cardiac surgery), heterogeneous (intensive care and emergency department) and chronic kidney disease (CKD) populations have supported the use of NGAL as an important biomarker in early diagnosis and prediction of duration and severity of AKI. NGAL differentiates AKI from changes in GFR due to chronic disease progression, predicts duration of ICU stay and provides prognostic value. Specifically, a single urine level of NGAL in the emergency department differentiates AKI from normal function and from pre-renal azotaemia, and predicts poor in-patient outcome.
A recent multicentre pooled analysis of published data on 2322 critically ill children and adults with the cardiorenal syndrome revealed the surprising finding that approximately 20% of patients display early elevations in NGAL concentrations but never develop increases in serum creatinine. Importantly, this sub-group of ‘NGAL-positive creatinine-negative’ subjects encountered a substantial increase in adverse clinical outcomes, including mortality, dialysis requirement, ICU stay and overall hospital stay. Thus, early NGAL measurements can identify patients with sub-clinical AKI who have an increased risk of adverse outcomes, even in the absence of diagnostic increases in serum creatinine.
Among acute decompensated heart failure patients, high admission serum NGAL levels were associated with increased risk of worsening RF. In particular, patients with an NGAL of >140 ng/mL on admission had a 7.4-fold increased risk, with a sensitivity and specificity of 86% and 54%, respectively. NGAL values are also significantly increased and parallel the clinical severity of CHF. After a 2-year follow up, patients with baseline NGAL > 783 ng/mL had a significantly higher mortality. These findings may suggest that NGAL plays a pivotal role in the systemic adaptation to CHF. Elevated baseline serum levels in acute post-myocardial infarction and CHF correlated with clinical and neurohormonal deterioration and adverse outcomes. In a rat model of post-MI HF, NGAL/lipocalin-2 gene expression was increased in the non-ischaemic left ventricle segments, primarily located to cardiomyocytes. Strong NGAL immunostaining was found within cardiomyoctes in experimental and clinical HF. Furthermore interleukin-1β and agonists for toll-like receptors 2 and 4 were potent inducers of NGAL/lipocalin-2 in isolated neonatal cardiomyocytes supporting a role for the innate immune system in HF pathogensesis. Urinary NGAL also increases in parallel with the NYHA classes for HF and is also closely correlated with serum NGAL, Cys-C, SCr and eGFR. This suggests tubular damage may accompany renal dysfunction in CHF, which has prognostic consequences.
Evidence is continuing to accumulate and NGAL measurement appears to be of diagnostic and prognostic value. In a recent meta-analysis, NGAL levels predicted renal replacement therapy initiation and in-hospital mortality. Several recent studies showing the response of urinary levels to therapy suggest a future role for NGAL for follow up and monitoring the status and treatment of diverse renal diseases reflecting defects in the glomerular filtration barrier, proximal tubule reabsorption and distal nephrons. Thus the prospects of NGAL being used as a diagnostic tool, even beyond the realms of nephrology, are exciting but require further clinical research. The commercial availability of standardised clinical platforms for the accurate and rapid measurement of NGAL in the urine and plasma will facilitate future investigations as well as direct clinical applications.
Interleukin-18
Interleukin (IL)-18 is a proinflammatory cytokine which induces interferon-g production in T cells and natural killer cells. It is synthesised as a biologically inactive precursor, which requires cleavage into an active molecule by an intracellular cysteine protease similar to IL-1b. IL-18 is both a mediator and biomarker of ischaemic AKI. Several early studies demonstrate increases in patients with acute tubular necrosis, prerenal azotaemia, nephrotic syndrome, delayed graft function after renal transplantation, chronic renal insufficiency and urinary tract infections. In contrast nephropathy, cardiopulmonary bypass, critically ill children and kidney transplantation, urinary IL-18 rises two days earlier than SCr. Urine IL-18 increases four to six hours after cardiopulmonary bypass, peaks at over 25-fold at 12 hours, and remains elevated up to 48 hours later. IL-18 levels also predict graft recovery and need for dialysis up to three months later. There is also significant evidence that IL-18 contributes to clinical HF and other acute and chronic cardiovascular presentations. Presently there are no studies with patients with CRS.
Major concerns over IL-18 surround its discriminatory capacity and appropriate use. One concern is a spill over into the urine and its effects as a confounder, differentiating elevated cardiac as opposed to renal injury. Additionally, serum IL-18 may be increased in other disease states e.g. autoimmune disorders such as SLE, certain leukaemias, postoperative sepsis, chronic liver disease and acute coronary syndromes. On a positive note serum IL-18 levels were not different between those with and without AKI post paediatric cardiac surgery, and data suggesting its pathophysiological contribution to the renal damage observed during ischaemia/reperfusion are positive signs for its discriminatory values and causative effects in renal injury. Thus IL-18 appears to be a worthwhile addition to a biomarker panel in the assessment of AKI.
Kidney injury molecule-1
Kidney injury molecule-1 (KIM-1) is a transmembrane protein that is highly over expressed in proximal tubule cells after ischaemic or nephrotoxic AKI. Several studies have shown KIM-1 in urine and renal biopsy to be elevated from predominately ischaemic AKI and not from prerenal azotaemia, chronic renal disease, and contrast nephropathy. KIM-1 appears to play a role in the pathogenesis of tubular cell damage and repair in experimental and human kidney disease. KIM-1 is a sensitive marker for the presence of tubular damage. It is virtually undetectable in healthy kidney tissue, but tubular KIM-1 expression is strongly induced in acute and chronic kidney disease as well as transplant dysfunction, where it is significantly associated with tubulointerstitial damage and inflammation. Elevated urinary KIM-1 levels are strongly related to tubular KIM-1 expression in experimental and human renal disease, indicating that urinary KIM-1 is a very promising biomarker for the presence of tubulo-interstitial pathology and damage. Furthermore, urinary excretion of KIM-1 is an independent predictor of graft loss in renal transplant recipients, demonstrating its prognostic impact. Studies after cardiopulmonary bypass surgery have noted similar findings. KIM-1 also predicts adverse clinical outcomes in various forms of AKI. Data from non-diabetic proteinuric patients suggest that urinary excretion of KIM-1 may have the potential to guide renoprotective intervention therapy. KIM-1 could potentially provide additional prognostic data for tubular damage in CHF. Future studies will reveal whether the sensitive biomarker KIM-1 will become a therapeutic target itself. Kim-1/KIM-1 dipsticks can provide sensitive and accurate detection of Kim-1/KIM-1, thereby providing a rapid diagnostic assay for kidney damage and facilitating the rapid and early detection of kidney injury in preclinical and clinical studies. The primary limitation of KIM-1 is that time to peak is 12 to 24 hours after insult. While it may be of limited use as an early AKI biomarker, the ability to detect KIM-1 in urine makes it an attractive option, possibly in a biomarker panel togther with NGAL and IL-18.
L-FABP
The fatty acid-binding proteins (FABPs) are 15kDa cytoplasmic proteins. There are two types: heart type (H-FABP) located in the distal tubular cells and liver type (L-FABP) which is expressed in the proximal tubular cells. Both markers have been suggested as useful for the rapid detection and monitoring of renal injury. H-FABP has been tested as a marker for ischaemic injury in donor kidneys. L-FABP has been tested in progressive ESRD as well as renal injury post renal transplantation and cardiopulmonary bypass and more recently acute coronary syndromes. In patients undergoing PCI for unstable angina, urine L-FABP levels were significantly elevated after two and four hours and remained elevated for 48 hours. SCr did not change significantly during the study period. Among nondiabetic CKD patients, urine L-FABP levels correlated with urine protein and SCr levels. Notably, L-FABP levels were significantly higher in patients with mild CKD who progressed to more severe disease. Neither SCr nor urine protein differed between those same groups. H-FABP however is produced by myocardial damage and its clearance is determined by RF. The ratio of H-FABP to myoglobin after haemodialysis may be a useful marker for estimating cardiac damage and volume overload in haemodialysis. This may be an advantage for FABP in a panel of biomarkers to discrimnate background noise and cases where troponin levels can’t be interpreted. The main drawbacks are lack of evidence in the HF setting, small sample sizes in existing studies, and non-availability of a commercially usable assay. Additional longitudinal studies are needed to demonstrate the ability of L-FABP to predict AKI as well as CKD and its progression in cohorts with CKD of multiple aetiologies.
Biomarker panels
Each of these biomarkers has advantages and limitations. It will be a while yet before any of these biomarkers match serum troponin and act as a ‘standalone’ marker. However they do provide a safety mechanism initially to highlight anticipated risk, as well as additional information on likely renal pathophysiology. It may ultimately be that a panel of biomarkers is required. Candidates for inclusion are NGAL, IL-18, KIM-1, Cys C and L-FABP. The alternative may be selective use of markers when renal injury is anticipated, a strategy synonymous with acute coronary syndromes with serial cardiac enzymes, i.e.’serial renal enzymes’. Ultimately a point of care device would be ideal, and some kits are already in place. It is however clear that the learning paradigm is still ongoing. Future studies will need to validate these biomarker panels in a large heterogenous cohort.
The future of renal assessments in cardiovascular patients
Renal dysfunction is an independent and significant contributor to poor heart failure outcomes. Idiosyncracies in cardiorenal physiology and limitations of conventional diagnostic tools are factors in the poor prescribing of proven heart failure therapies in these patients. Novel biomarkers of renal injury and function are currently available. These biomarkers do have limitations but they address gaps in the information gained from conventional biomarkers i.e. improvements in injury chronology and functional accuracy. Significant limitations in how these markers are used as well as issues of availability and cost can only be addressed by further work. Future research studies should consider addressing these questions.
Reference
Abstracted with permission from Iyngkaran P et al. Cardiorenal syndrome – definition, classification and new perspective in diagnostics. Seminars in Nephrology 2012; 32: 3-17.
Helping elite athletes to give a peak performance
, /in Featured Articles /by 3wmediaAccording to applied physiologist Dr Brian Moore, and Dr Andrew Hodgson, Consultant Physician (Haematology) – co-founders of the Irish company ORRECO – one of the most difficult elements of competing in sport at a world class level is to balance training hard whilst ensuring adequate recovery. Dr Moore and his integrated team of high performance practitioners advised Olympic medalists and competitors at the last three Olympic games, and will do the same at the London Olympic games this year. CLi spoke to Dr Moore and his team to find out more about ORRECO’s mission and the methods it uses to help athletes reach peak performance without overtraining.
Q. Could you first tell us a little about your company. What inspired you to set up ORRECO and what did you hope to achieve? Briefly how does the company operate?
ORRECO was founded with the aim of joining the disciplines of clinical and sports haematology to deliver a unique proposition for world sport. We facilitate blood and saliva analysis for some of the world’s best athletes from an administrative base on Ireland’s western coast – the Innovation Centre at the Institute of Technology, Sligo.
Analysis occurs through a global network of partner laboratories that are located close to training (altitude, warm weather) and competition (World Cup, Championship, Olympic) venues. Results are reported in real time through our software solution DAVE (Download, Analyse, Validate and Export your results) to allow team physicians, coaches and performance staff to review information immediately and compare the results to an athlete’s performance. We cross-reference the results with training and competition data, (e.g. speed and power, GPS tracking) to understand the individual’s adaptation to training.
Recognising that testing and result reporting are just one part of the solution; we also provide a consultancy service for elite athletes and their teams. Our performance staff assists in interpretation and comparison of results against sports-specific reference ranges, as well as provides practical guidance and interventions where needed. This includes nutritional support, training-plan modification and more. Rather then rely on one specific biomarker, we use multiple assays that are aggregated by our bio-statisticians and map the athlete on a range from ‘well’ to ‘unwell’, and, from ‘peak performance’ to ‘over-reached’ or ‘over trained.’
Q. Tough training programmes are integral to sporting success, but what are the main problems that can occur if athletes over train?
We know that in the elite sport world, very small margins exist between defeat and victory. To succeed, an athlete must train extremely hard, and there are situations when a training programme requires an athlete, player or squad to be selectively overreached or overloaded for a short time period. With a subsequent, controlled reduction in training volume, a super-compensation occurs, allowing for a positive adaptation to the intense training dose and overall improved performance.
However, if athletes train too hard for too long in their pursuit of success, they will eventually fatigue and follow the performance continuum [Figure 1], which leads to injury and increased frequency of illness, such as upper-respiratory tract infections, immunosuppression, disturbed sleep patterns and depressed mood states. Biomarker analysis can help navigate the fine line required to balance adequate load with sufficient recovery.
Q. How did you establish which biomarkers were the most important for monitoring athletes in training and how do you carry out analysis of these biomarkers?
Our starting point is leveraging clinical markers that are routinely used for general health and wellness. In the context of training, we rely on biomarkers found in blood and saliva that are known signs of a normal process (e.g. adaptation), abnormal process (e.g. maladaptation), a particular condition (e.g. under performance syndrome) or disease (e.g. infection).
Biomarkers may be used to see how well the body responds to an intervention/process (e.g. training modification), a treatment (e.g. recovery solution) or a stress inducer (e.g. game, match). Our specialist team includes former speed and power coach to the New Zealand ‘All Blacks’ and Americas Cup sailing team, Dr Christian Cook; the first team physiologist to Real Madrid, Dr Carlos Gonzalez-Haro; the former Director of the Australian Institute of Sport Haematology Lab, Robin Parisotto; and Clinical and Performance Nutritionist to the British Olympic Team, Nathan Lewis (MSc). We have significant collective experience of applying, analysing and interpreting biomarkers across a range of elite sports at the very highest level of world competition. We facilitate analysis of markers that have been applied and validated in the world of elite sport. Our combined experience of working with thousands of elite athletes and monitoring them at key times during the season means we can discern trends that are consistent with either peak, or, at times, underperformance. We are especially interested in athletes’ cell counts, inflammatory markers, trace metal status, immunoglobulins and hormonal profiles.
Q. Are you satisfied with the methods and equipment used?
We are constantly looking for improvement and searching for markers that can give us objective information about an athlete’s response capabilities and/or status. For example, we utilise the routine parameters, including the differential WBC, haemoglobin and reticulocyte counts, available on the Siemens Healthcare Diagnostics ADVIA 2120 Haematology System, to give us rapid insights into an athlete’s health and wellness. We also rely on additional parameters available on this platform, such as the cellular haemoglobin of the reticulocyte (CHr) and the percentage hypochromasia of both the reticulocytes and mature red cells (%hypor and %hypom). These parameters are also routinely utilised in renal medicine to deliver specific information about the quality of erythropoiesis.
Historically, we would have used ferritin to assess the iron stores, but given the acute phase response of the parameter, we interpret the result in concert with the white cell counts and creatine kinase (CK), as we know the parameter is elevated in infection and inflammation. This information is especially important when an athlete is undertaking altitude or endurance training, as we can ensure enough iron is being made available to the developing red cells and they benefit from all their hard work. We can also pick up a functional or pre-latent iron deficiency before it impacts upon performance and track the responses to prescribed iron supplementation. Thus, in addition to looking for new techniques, we also seek to apply established principles in new ways.
Q. How do you see the future for sports medicine in general and ORRECO in particular?
As explained by our colleague, Dr Bruce Hamilton, sports medicine is no longer focused on just treating injury and illness in athletes. Increasingly, early recognition and prevention of injury and illness is the goal. Particularly when working with elite athletes, being able to identify athletes at risk of developing problems is a constant challenge, and vast amounts or research and resources are being directed at this task. Despite this, we are only just beginning to understand the risk factors behind even common injuries (e.g. hamstring muscle strains) and techniques that may be used to prevent them. Similarly, while illness and fatigue have been recognised as significant limitations to elite athletic performance for many years, to date, the understanding of risk factors and the ability to identify athletes at risk has been limited by both our knowledge base and our technical ability. The goal of tools, such as those developed by ORRECO, are to facilitate the identification and prevention of illness in highly tuned athletes, thereby allowing them to compete to the best of their ability. This is consistent with the aspirations of modern sports medicine around the world.
By integrating sports haematology and biochemistry with knowledge and expertise in clinical and performance nutrition, applied physiology, speed and power physiology, biostatistics and cellular nutrition across our team, whole avenues of possibility open up to performance science in general. ORRECO aims to provide a global resource for real-time sports haematology and biochemistry results for athletes training and competing around the world.
For more information go to www.orreco.com. An introductory video can be seen at http://vimeo.com/41485500.
Siemens Healthcare Diagnostics
Book Review
, /in Featured Articles /by 3wmediaParasitology: An Integrated Approach
Ed. by Alan Gunn and Sarah Jane Pitt, Pub. by Wiley-Blackwell 2012, 456 pp, €41.80
www.wiley.co.ukThis book provides a concise, student-friendly account of parasites and parasite relationships that is supported by case studies and suggestions for student projects. The book focuses strongly on parasite interactions with other pathogens and in particular parasite-HIV interactions, as well as looking at how host behaviour contributes to the spread of infections. There is a consideration of the positive aspects of parasite infections, how humans have used parasites for their own advantage and also how parasite infections affect the welfare of captive and domestic animals. The emphasis of the book is on recent research throughout and each chapter ends with a brief discussion of future developments. This text is not simply an updated version of typical parastitology books but takes an integrated approach and explains how the study of parasites requires an understanding of a wide range of other topics from molecular biology and immunology to the interactions of parasites with both their hosts and other pathogens
Clouds in the lab
, /in Featured Articles /by 3wmediaLike much in healthcare IT, the development of Laboratory Information Management Systems (LIMS) has been an uneven mix of technology-push and user-pull, coupled with regulatory efforts at streamlining the two. Today, the new vista of cloud computing is rapidly opening up new LIMS opportunities, especially for smaller labs.
The demand for LIMS began in the late 1970s after the proliferation of electronic lab equipment and an explosion in data. The then-emerging technology of ‘minicomputers’ offered LIMS the first realistic alternative to expensive/inaccessible mainframes. Minicomputers, however, were only a brief interlude in computing technology, before the advent of personal computers. Most minicomputer vendors (e.g Data General, Wang, Norsk Data etc.) have since disappeared. By the late 1980s, personal computers enabled LIMS users to leverage relational databases. The arrival of client/server architecture and the Internet in the 1990s expanded the reach of LIMS outside laboratories, providing novelties such as 24×7 analysis from offshore locations. The past decade has expanded the footprint of LIMS further via Wi-Fi, mobile access and standards like XML.
However, much of this has been a mixed blessing. As the LIMS community proliferated, so too did concerns about data security and systems complexity. Competition among LIMS vendors led to a blizzard of new features, ranging from those required to comply with regulations, to a swathe of pureplay ‘business’ applications such as inventory and personnel management, workflow sequencing etc. The result: an escalation in user expectations, and in entry-level costs.
In spite of the recent centralisation of healthcare, most labs are still relatively small. In the US, the largest 50 account for one-third of the industry’s total revenues of about 40 billion dollars; over 7,500 labs share the rest. With commercial LIMS systems beyond their budgets, several labs have sought to develop their own, but almost always ended up with huge cost-overruns, and performance problems. One reason lies in the very essence of information technology, namely the steady fall in unit costs of processing power, with savings harnessed by commercial vendors to bundle additional features. The second reason: any mission-critical IT system needs to handle peak load requirements, often several multiples of the median; healthcare is no exception.
Cloud computing technology may answer both the above challenges, and LIMS seems an especially promising area. At its most basic, cloud computing is akin to an electricity grid, pooling computing horsepower across locations to enable scale-up on demand; the parallel is particularly close in terms of load balancing – the ability to adjust database, server and networking capacity to fluctuating demand.
In May 2010, a headline feature by the American Chemical Society titled ‘LIMS in the Cloud’ emphasised how cloud computing was opening up LIMS to small labs, which had ‘not been particularly well served’ by vendors. Indeed, cloud-based LIMS pioneers such as LabLynx have acquired over 1,000 customers in less than two years of launch. The recent entry of IT giants such as Microsoft, Oracle and Google into cloud computing promises to galvanise the industry further, with LIMS applications likely to remain at the forefront.
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, /in Featured Articles /by 3wmediaFind your way with Freelite and Hevylite
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