Mannitol clearance for assessment of glomerular filtration rate in critically ill patients

Introduction In critically ill patients, accurate measurements of glomerular filtration rate (GFR) are challenging and commonly used GFR estimation equations based on a single serum creatinine measurement perform poorly. In this study, we evaluated mannitol as a clearance marker for measuring GFR in intensive care unit (ICU) patients. Multi-sample plasma clearance of the radiocontrast agent, iohexol, served as the reference method. Methods Twenty ICU patients received simultaneous bolus injections of mannitol and iohexol. Blood samples for marker concentrations were collected over five hours. Marker concentrations were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). For both markers, GFR was assessed by the Bröchner-Mortensen multi-sample calculation model. In addition, plasma clearance for mannitol was assessed by the one-sample Jacobsson equation, for samples taken 4 and 5 h after the bolus injection. Agreement between clearance methods was assessed by the Bland-Altman method and accuracy of mannitol by calculating P30 and P10. Results The bias between mannitol and iohexol clearances was 2.9 ± 9.3 ml/min/1.73 m 2 , corresponding to 6% of the reference value, with an error of 39%. The accuracy for mannitol clearance vs. the reference method was 85% (P30) and 60% (P10), respectively. The corresponding values for bias, error, P30 and P10 for the one-sample plasma clearance of mannitol at 5 h, were: 0.9 ± 8.0 ml/min/1.73 m 2 , 32%, 84% and 68%, respectively. Conclusions In critically ill patients, plasma clearance of mannitol showed acceptable agreement with iohexol clearance, for both multi-and single-sample measurements.