Stability of Middle Molecule Clearance

Inclusion Criteria: * informed consent * age\>18 years * acute renal insufficiency with indication for continuous hemodialysis, according to RILFE classification F: serum creatinine increase \> 3-fold or serum creatinine \> 4mg/dl with acute increase of \>0,5mg/dl Urine Output \<0,3mg/kg/h for 24 h or anuria for 12 h * body weight:60-80kg * anticoagulation with citrate possible and indicated * Dose for hemodialysis of 2l/h Exclusion Criteria: * participation in another clinical trial within on month prior to this study * pregnancy or brest feeding * septic shock * interference with cystatin-C 1. haemolysis \<1g/dl 2. Bilirubin\<9mg/dl 3. Triglyceride \>700mg/dl 4. rheumatoid factor \> 300kIU/l