Clearance of mannitol for assessment of glomerular filtration rate in chronic kidney disease: A validation against iohexol clearance

This study evaluates mannitol as a clearance marker for measuring glomerular filtration rate (GFR) in outpatients with chronic kidney disease (CKD). Multi-sample iohexol clearance served as the reference method. Twenty patients with CKD, stages 3-4, received bolus injections of both clearance markers simultaneously. Blood samples were collected 3, 5 and 22 h after the bolus injections. Marker concentrations were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). A calculation template, based on the Bröchner-Mortensen multi-sample model, was applied to determine GFR for both markers. In addition, plasma clearance of mannitol was assessed using the one-sample Jacobsson equation, applied to samples taken 5 and 22 h after the bolus injection of mannitol. Agreement between the clearance methods was assessed by the Bland-Altman method, and the accuracy of mannitol clearance versus iohexol clearance was assessed by calculating P30 and P10. For the multi-sample clearance, the between-methods bias was 0.95 ± 1.4 mL/min/1.73 m², the error was 10%, and the accuracy was 100% for both P30 and P10. The corresponding values for bias, error, P30 and P10 for the one-sample plasma clearance of mannitol versus the reference method were: -2.3 ± 3.6 and 2.9 ± 3.0 mL/min/1.73 m², 24% and 21%, 95% and 100%, 80% and 60%, respectively for samples obtained 5 and 22 h after the bolus. Mannitol exhibited a reliable performance as a clearance marker in patients with CKD, stages 3-4, and may serve as an alternative when standard markers, iohexol or isotopes, are contraindicated. However, further large-scale studies are required to confirm these findings.