Comparison of Two Different External Clearance Markers - Mannitol and Iohexol for Measuring Glomerular Filtration Rate

Overview

GFR is the best parameter of the real kidney function. Measurements, however are time-consuming and have limited capacity. Patients treated in the intensive care units often have more than one organ-insufficiency and acute kidney injury (AKI) has an incidence of up to 70 %. GFR changes dynamically and this is one of the reasons why GFR-measurements have limited indications on the ICU. Retention of medicines or their active metabolites, however can lead to side effects, toxicity and or prolonged ICU-stay. Moreover, patients with allergy to actually standard marker, contrast material iohexol, or gravid patients are not candidate for measuring GFR with iohexol. In this prospective clinical trial two exogen marker substances will be compared, mannitol as a new marker and iohexol as a standard marker for measuring glomerular filtration rate (GFR). Patients in the intensive care units (ICU) and an outpatient group with stable chronic kidney disease (CKD) are included. The main question is, how reliable mannitol-GFR is compared to iohexol-GFR in a wide range of kidney insufficiency. GFR measurements are performed with a bolus injection technique. Patients get mannitol and iohexol bolus at time zero and blood samples are taken three times according to local protocols for iohexol clearance measurements.

Written inform consent from the patients or their relatives if they can not communicate. Inclusion criteria: Patients with acute or acute on chronic kidney failure (AKI, CKD), who are treated in the intensive care units because of any kind of organ insufficiency are enrolled. Stabil circulatory parameters needed with or without vasoactive drugs. Continuous intravenous administration of fluids and drugs without significant changes during the study period. Exclusion criteria: Unstable circulation and need for fluid resuscitation. Known extracellular volume expansion as ascites or peripheral edema. Intravenous paracetamol administration between or during the measurement period. Measurement with iohexol as contrast material during the previous days. Missing inform consent. Allergy to contrast material. Sample taking: at time zero and three times after the bolus injection. Timing is scheduled according to the local protocol for iohexol-GFR calculation. Samples are coded and can not identified when results are published. Outcome measures: Is mannitol clearance a reliable method for measuring GFR compared to iohexol-clearance? Comparing the two methods with Bland-Altman plots and statistical calculation for accuracy P30 and P20.