Clinical microbiology laboratories were central to the tough but successful fight against infectious diseases in the 19th and first half of the 20th centuries, and resonate in the names of now-iconic figures from Jenner, Pasteur and Lister to Koch, Gram and Fleming.
Vitamin D is derived from food, and human beings need exposure to sunlight for its synthesis. This is achieved through the absorption of ultraviolet B radiation by 7-dehydrocholesterol in the skin. However, certain sections of the population cannot produce Vitamin D in sufficient quantities; such at-risk groups are the focus of screening.
The principal function of Vitamin D is to enable absorption of calcium and phosphorus and promote bone health. It is metabolized in the liver to 25-hydroxyvitamin D (25OHD). The kidneys activate 25OHD to 1,25-dihydroxyvitamin D, which in turn regulates calcium, phosphorus and bone metabolism.
25OHD is the key circulating form of vitamin D, and as a biomarker, is generally the target of screening.
The deforming condition known as rickets, caused by a deficiency of Vitamin D, was a scourge in children until the early 20th century. The vitamin was identified in the 1920s. Though the crucial role played by sunlight in avoiding rickets had been known since the 1820s, it was only endorsed officially after over a century. Accompanied by fortification of milk and infant food with Vitamin D, rickets in industrialized countries soon became a thing of the past.
Rickets has, however, recently returned. One reason is ironic: the excessive promotion of breastfeeding and an unawareness that human milk does not suffice for an infant’s Vitamin D needs. This is exacerbated by modern lifestyles which discourage exposure to the sun, along with an overuse of sun screens and other forms of protection.
Benefits likely for several diseases
More recently, researchers have found that Vitamin D may also play a role in controlling a host of other diseases. This has revived the debate about screening.
Diseases against which Vitamin D provides benefits role are believed to include cancer, cardiovascular and cerebrovascular disease, diabetes and metabolic disorders, multiple sclerosis, inflammatory bowel diseases and certain neurological conditions.
Ethnicity, age and gender
Since the mid-1980s, it is accepted that Vitamin D’s role in the context of certain major medical conditions depends on ethnicity. The re-emergence of rickets has been concentrated, for example, in African Americans in the US and Asians in the UK.
In 1988-1994, the third US National Health and Nutrition Examination Survey (NHANES III) found significant differences between different ethnic groups in terms of 25OHD levels, which in turn correlated to a predisposition to both high blood pressure and diabetes.
In 2002, researchers found that Vitamin D’s role in pediatric Crohn’s disease was particularly pronounced in African-American children. Likewise, in the case of coronary artery disease, one high risk group consists of African-Americans with HIV.
Age-specific risks too are an area of concern. The elderly have been specifically targeted to study Vitamin D’s role in hypertension and in cognitive decline. Older women, in particular, seem prone to suffer from its deficiency, and thereby to adverse effects on their musculoskeletal system.
On the other side of the age scale, Vitamin D deficiency in infants seems associated with a range of chronic diseases in later life, from multiple sclerosis to Type 1 diabetes and schizophrenia.
More research still needed
Nearly all the research efforts cited above add caveats to their findings, underlying the role of Vitamin D in avoiding several diseases, but also calling for further investigation. Two recent meta-studies, which assimilate the results of previous research in this area, illustrate the problem.
One meta-study, published at the end of 2012, focuses on Vitamin D and cardiovascular disease (CVD). Its scope extends to 19 previous studies covering 6,123 CVD cases in nearly 66,000 subjects. It notes that, in spite of evidence about a link between CVD and Vitamin D deficiency, “optimal” levels of 25OHD for cardiovascular health “remain unclear,” and underlines that there is a “generally linear, inverse association” between circulating 25OHD in the range of 20-60 nmol/L and a risk of CVD. However, it calls for “further research” on 25OHD levels higher than 60 nmol/L.
The second meta-study dates to the end of 2013 and covers 18 prospective studies on Type 2 diabetes and metabolic disorders, involving 210,107 participants. It begins by observing that though “several studies have assessed Vitamin D in relationship with metabolic outcomes”, “results remain inconsistent.” It concludes that Vitamin D-targeted interventions “may be a useful preventive measure for metabolic diseases”, but also warns that “reliable evidence from carefully designed intervention studies, particularly those based on healthy populations, is needed to confirm observational findings.”
Differences in definition of risk persist
This bewildering array of qualifiers makes screening for Vitamin D problematic, for now.
Making things even more di ficult are continuing doubts about what level of 25OHD indicates a risk, and for who, when and where.
In the UK, the National Health Service (NHS) considers concentrations of less than 25 nmol/L to indicate “deficiency”, with “insufficiency” at 25-50 nmol/L, and “adequate” levels at more than 50 nmol/L. The American Journal of Clinical Nutrition (AJCN) specifies 25OHD below 50 nmol/L as an indicator of “deficiency”, while 51–74 nmol/L does so for “insufficiency”; the 74 nmol/L margin (as discussed below) has also been adopted in Poland. On its part, the National Institutes for Health (NIH) defines less than 30 nmol/L as “deficiency”, 30-50 nmol/L as “generally considered adequate” and more than 125 nmol/L to be associated with “potential adverse effects.”
Although the NIH says a 50 nmol/L concentration covers the needs of 97.5% of the population, it still leaves 7.5 million Americans in need of screening.
Seasonal factors confound the playing field further. In the UK, for example, the “insufficiency” concentration of 25-50 nmol/L for 25OHD is found in as much as half the country’s population, during spring.
Last but not least are doubts about the relevance of 25OHD concentration itself. For instance, the European Food Safety Authority (EFSA) stated, as recently as 2012, that while it “is a good marker of vitamin D status”, 25OHD can only be used “as a biomarker of vitamin D intake in people with low exposure to sunlight.”
Recommendations for screening
In the face of this, there is little consensus about screening for Vitamin D.
Nevertheless, national recommendations to prevent Vitamin D deficiency were instituted in Poland in 2009, and three years later in Hungary and Germany. Underlying the ongoing lack of clarity on the issue, the German Nutrition Society, which issued the recommendations, also evaluated Vitamin D as part of a separate investigation into vitamin availability, but this time was sanguine, except in the elderly. The elderly were also the subject of nutrition recommendations by the the International Osteoporosis Foundation in 2010.
In much of continental Europe, 50 nmol/L of 25OHD concentration is used to indicate Vitamin D sufficiency, in line with Britain’s NHS and the US NIH. However, most east and central Europeans tend to follow the 2009 Polish recommendations, which specified less than 50 nmol/L as deficiency, 50-75 nmol/L as ‘suboptimal’, with an ‘optimal’ target of 75–125 nmol/L; the latter straddles the lower and higher margins prescribed in the US by the AJCN and NIH, respectively (see above).
Iterations on thresholds, meanwhile, continue to proliferate, even with regard to at-risk populations. For example, while both Germany and the International Osteoporosis Foundation suggest 25OHD concentrations of 60 nmol/L in the elderly, in 2013 the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis (ESCEO) recommended 50nmol/L for elderly women, and 75 nmol/L for “fragile” subjects.
The VITAL trial
It is to be hoped that many questions about the precise role of Vitamin D in battling some of the largest challenges facing modern medicine are answered in the years to come.
One such effort has, in fact, recently been launched. Known as VITAL (‘VITamin D and OmegA-3 TriaL), this interventional, randomized clinical trial is recruiting 20,000 men and women in the US to investigate whether daily dietary supplements of Vitamin D or omega-3 fatty acids reduces the risk of cancer, heart disease and stroke in people with no prior history of these illnesses.
Targeted supplementation most likely course
The above developments indicate that the argument about routine supplementation making “more sense” than screening is likely to yield place to “targeted” screening for at-risk populations, with an especially strong case for the elderly and infants.
Both groups were, in fact, highlighted in July 2011 Clinical Practice Guidelines on Vitamin D by the influential US-headquartered Endocrine Society. The Society also included “pregnant and lactating women,” “obese children and adults”, and patients on “anticonvulsant medications, glucocorticoids, antifungals such as ketoconazole, and medications for AIDS.”
Standardizing lab tests
In the meanwhile, one major concern for clinical laboratories with regard to Vitamin D tests seems to have been addressed. Until recently, serum 25OHD concentrations showed considerable variations, depending on the type of assays used (the most common is liquid chromatography). This led to differences among laboratories in their findings. The implication of such differences has been significant, especially given the differences in definitions of Vitamin D sufficiency and insufficiency.
In 2009, the US National Institute of Standards and Technology (NIST) released SRM 972, a reference material for 25OHD. SRM 972, updated by NIST in February 2013 to SRM 972a, is also used in Europe.
Developed countries have not escaped the rise in cases of multidrug-resistant tuberculosis. In the UK a mobile X-ray unit has been operating in London since 2005 and this service has been augmented with point-of-care testing (POCT) since 2011. POCT has been well received by patients and has greatly reduced the number of unnecessary hospital visits.
by Dr R. J. Shorten and Dr A. Story
Background
Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis. TB is primarily a respiratory disease, although it can affect any part of the body and it is spread from person to person via expectorated droplets by individuals with active pulmonary disease. TB is a significant international problem and in 1993 the World Health Organization declared tuberculosis a global emergency [1]. In 2012 there were 8.6 million new cases and 1.3 million deaths, the vast majority of these occurring in Asia and sub-Saharan Africa [2].
Multidrug-resistant TB
This global epidemic is further complicated by the increase in drug resistant M. tuberculosis. Multidrug-resistant TB (MDR-TB) is a form of TB caused by bacteria that do not respond to, at least, isoniazid and rifampicin, the two most effective, first-line anti-TB drugs. There were approximately 450 000 cases of MDR-TB globally in 2012. More than half of these cases were in India, China and the Russian Federation [2].
This epidemic has not been avoided in developed countries and following a century of decline, the incidence of TB in the UK has been rising since 1988. Data from Public Health England [3] shows that the majority of these cases are concentrated in urban areas, with almost 40% being in London (3426 cases in 2012). Additionally, one or more of the following risk factors were present in 7.3% of cases; history of problem drug use, alcohol misuse/abuse, homelessness or imprisonment. Furthermore, some of these individual risk factors are associated with smear positivity (those patients who are more likely to be contagious), drug resistance, poor adherence to treatment and loss to follow up [4]. Indeed, the growing problem of TB in these hard-to-reach groups has led to specific UK guidance [5].
Searching for patients
Find & Treat was established in 2005 to strengthen TB control in the socially excluded communities of London by working with over 200 partner organizations. The service has been evaluated as an innovative and cost-effective health and social care model [6]. The mobile X-ray unit (MXU) has been operating in London since this time and screens approximately 8000 patients per year (Fig. 1). It is staffed by TB nurse specialists, reporting radiographers, social workers and outreach workers and former TB patients with a lived experience of homelessness who work are Peer Educators. Its role is to identify hard-to-reach patients with suspected TB using digital chest radiographs. These patients are then linked into local healthcare provision via Accident & Emergency (A&E) departments or community TB programmes. In December 2011 the service was augmented with the Xpert MTB/RIF assay (Cepheid, Sunnyvale, California, USA), which was used as a point-of-care test (POCT) for the molecular detection of M. tuberculosis in sputum [7].
Point-of-care testing
Prior to the implementation of the Xpert assay, if a digital chest radiograph indicated active pulmonary TB (seen in 1–2% of patients screened), then the patient underwent immediate referral to the nearest hospital with a TB service. This involved a TB nurse specialist or outreach worker accompanying the patient to an A&E department for assessment, conventional microbiological investigation and possible admission. Approximately 20% of referred patients are subsequently confirmed to have TB and are initiated on a complex course of multiple antibiotics over a period of at least 6 months [8].
The Xpert MTB/RIF assay is a nucleic acid amplification test (NAAT). The easy to use analyser extracts, amplifies and detects DNA of M. tuberculosis in the patients’ sputum. The assay also detects approximately 95% of the common rifampicin resistance-conferring mutations in the rpoB gene (a surrogate marker of multidrug resistant TB) [9].
The hands-on time of the assay is minimal and a specimen container with a rubber septum in the lid allows the staff on the MXU to safely process sputum samples without the need for containment facilities or a microbiological safety cabinet (Fig. 2). MXUs exist in other European cities, but we believe that this is the first example of a NAAT POCT being used in this way anywhere in Europe.
Patients with abnormal X-rays that indicate active pulmonary TB are asked whether they can produce sputum. Those who can, expectorate a sample into the specific sample container. They seal the container and return it to the team on the MXU who assess the sputum for quality (sputum, rather than watery saliva is required). The sample reagent is carefully added through the rubber septum in the lid and swirled gently to allow homogenization of the sample. This process ensures that minimal aerosols are generated and that they are not released to cause exposure to the operator. The assay takes approximately 2 hours in total and the result will determine whether the patient requires immediate referral to a TB service. Patients with negative NAAT are followed up by two further sputum samples, including one early morning specimen, collected in the community and processed for routing smear microscopy and culture in hospital laboratories. Due to the high negative predictive value of the assay (94%) and the increased sensitivity compared to sputum microscopy [10], it is highly unlikely that any infectious cases will go undetected using this algorithm.
Considerations and advantages of POCT for TB
As the POCT is performed by non-laboratory staff, it is imperative that the MXU staff are comprehensively trained and assessed for competence. None of the staff had any laboratory or analytical experience prior to the implementation of this assay. Registered clinical laboratory staff are involved in all stages of implementation and training. A close working relationship between the MXU team and the clinical laboratory is required to ensure appropriate refresher training and review of standard operating procedures and risk assessments.
The assay has been well received by patients, particularly as a negative result prevents a referral to hospital. This allows MXU staff to focus resources on screening more patients, rather than accompanying patients to hospital who subsequently are confirmed to be clear of TB. The MXU regularly screens in custodial settings where capacity to effectively isolate suspected cases is limited and significant resources are required accompanying patients with suspected TB to hospital appointments for further investigations. The value of the assay in determining which patients are potentially infectious is especially useful in these settings. The ability of the Xpert MTB/RIF to detect most cases of rifampicin resistant (and therefore likely to be MDR) TB, allows the MXU team to initiate appropriate second-line therapy more rapidly. Additionally, the simplicity and safe use of the assay has been well adopted by the MXU staff. We have demonstrated the potential of this technology in focussing resources on the most appropriate individuals and therefore improving the quality of care in this vulnerable group of patients. A randomized controlled trial to assess the benefit of using this assay on patients with an abnormal chest X-ray against them being referred to secondary care is underway to accurately quantify the benefits of this assay in tackling TB in this group of patients.
Summary
The epidemiology of TB in 21st century big cities is characterized by a concentration of disease in hard-to-reach medically underserved populations. Capacity to outreach effective diagnostic platforms directly to high risk populations is likely to become an increasingly important feature of TB control [11].
References
1. World Health Organization (WHO). Tuberculosis. Fact sheet 104, 2012. 2. WHO. Tuberculosis. Media centre; Fact sheet 104, 2014.
3. Tuberculosis in the UK: Annual report on tuberculosis surveillance in the UK, 2013. London: Public Health England 2013.
4. Story A, Murad S, Roberts W, et al. Tuberculosis in London: the importance of homelessness, problem drug use and prison Thorax 2007; 62(8): 667–671.
5. National Institute for Health and Clinical Excellence (NICE): Public health guidance. Tuberculosis – hard-to-reach groups. PH37 2012.
6. Jit M, Stagg HR, Aldridge RW, et al. Dedicated outreach service for hard to reach patients with tuberculosis in London: observational study and economic evaluation. BMJ 2011; 343: d5376.
7. Boehme CC, Nabeta P, Hillemann D, et al. Rapid molecular detection of tuberculosis and rifampin resistance. N Engl J Med. 2010; 363: 1005–1015
8. NICE: Clinical guidelines. Tuberculosis: Clinical diagnosis and management of tuberculosis, and measures for its prevention and control. CG117 2011. (http://guidance.nice.org.uk/CG117)
9. Zhang Y, Yew WW. Mechanisms of drug resistance in Mycobacterium tuberculosis. Int Tuberc Lung Dis. 2009; 13(11): 1320–1330.
10. O’Grady et al. Evaluation of the Xpert MTB/RIF assay at a tertiary care referral hospital in a setting where tuberculosis and HIV infection are highly endemic. J Clin Infect Dis. 2012; 55(9): 1171–1178.
11. van Hest NA, et al. Tuberculosis control in big cities and urban risk groups in the European Union: a consensus statement. Euro Surveill. 2014;19(9): Article 7.
The authors
Rob J. Shorten1* BSc, MSc, PhD and A Story2 RGN MPH PhD
1Clinical Scientist, Department of Medical Microbiology, Central Manchester Foundation Trust and Honorary Research Associate, University College London Centre for Clinical Microbiology, UK
2Clinical Lead Find & Treat, University College Hospitals NHS Foundation Trust, London, UK
*Corresponding author
E-mail: rob.shorten@nhs.net
November 2025
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