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.
