Patients Undergoing Continuous Renal Replacement Therapy (CRRT)
Hutten et. al.1 found that patients receiving CRRT with citrate anticoagulation had normal tMg levels, but low iMg levels. This is due to magnesium ions being bound by citrate, and the citrate-magnesium complex being measured as tMg. These patients are actually hypomagnesemic but would not be recognized as such if only tMg were measured.
Surgical ICU Patients
Yeh et. al.2 found that 21% of tMg tests which were reported as normal were hypermagnesemic based on iMg.
This exposes patients to potential risks associated with undetected hypermagnesemia, including prolonged
days on the ventilator, muscle weakness, QT prolongation, and cardiac arrhythmia. In addition, there were many
patients with low tMg and normal iMg, which led to unnecessary Mg supplementation and repeat blood draws.