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 m2, 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 m2, 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.