Cystatin C as a marker of residual renal function during continuous hemodiafiltration.

Background: The level of residual renal function (RRF) has an important impact on follow-up in critically ill patients with renal failure. There is currently no clear marker of RRF.

Methods: Cystatin C (cysC) concentrations were measured before and during the first 48 h of CVVHDF in 33 mechanically ventilated patients suffering from renal failure. Samples were drawn both from the ports proximal and distal to the filter. Each of the two control groups consisted of 10 patients.

Results: The levels of cysC were significantly higher in the group where diuresis (Vu) remained low or decreased after 48 h of treatment (n = 21, Vu median 380 (80-935) ml/24 h, cysC range 4.44-3.42 mg/l) than in the group where Vu increased to the level of 1.5 ml.kg(-1).h(-1) or higher after 48 h of treatment (n = 12, Vu 4,570 (4,000-5,130) ml/24 h, cysC 3.17-2.46 mg/l, p < 0.01). Creatinine clearance taken before treatment was not different between the groups. Significant correlation between cysC levels and Vu was found (r = -0.44, p < 0.0001). CysC levels were significantly higher in non-survivors than in survivors (3.54 +/- 1.38 vs. 3.07 +/- 1.24, p < 0.03).

Conclusion: The levels of cysC are inversely related to Vu. High levels of cysC are associated with low residual diuresis, longer duration of CVVHDF and higher intensive care unit mortality in patients treated with CVVHDF.