Cystatin C and Kidney Function Recovery in Patients Requiring Continuous Kidney Replacement Therapy for Acute Kidney Injury

Background: Plasma cystatin C is a reliable marker to estimate kidney function; however, it is unknown whether this remains true in patients receiving continuous kidney replacement therapy (CKRT). Herein, we tested the hypothesis that lower concentrations of plasma cystatin C during the first three days of CKRT would predict kidney function recovery. Methods: We performed a retrospective observational study of 72 patients from a 126-patient, single-center CKRT study. We studied two a priori defined cohorts of patients without advanced CKD who had acute kidney injury requiring CKRT (AKI-CKRT): 1) with early kidney function recovery defined as liberation from KRT within seven days of CKRT initiation versus 2) with delayed kidney function recovery defined as receipt of KRT for >21 days or death while on KRT. Subsequent analysis included patients with advanced CKD and intermediate kidney function recovery (liberation between 8 and 21 days). Cystatin C was then measured on stored plasma, urine, and dialysis effluent collected prior to CKRT initiation and on days 1, 2, and 3 of CKRT. Results: Plasma cystatin C was significantly lower in patients with early kidney function recovery in comparison to patients with delayed kidney function recovery on days 1 (1.79 vs. 2.39mg/L), 2 (1.91 vs. 2.38mg/L) and 3 (2.04 vs. 2.67mg/L) of CKRT. Sieving coefficient and CKRT clearance of cystatin C were similar for patients with early and delayed kidney function recovery. The lowest plasma cystatin C concentration on days 1-3 of CKRT predicted early kidney function recovery with an area under the receiver operating curve of 0.77 (P = 0.002), positive likelihood ratio of 5.60 for plasma cystatin C <1.30mg/L, and negative likelihood ratio of 0.17 for plasma cystatin C ≥1.88mg/L. Conclusion: Lower plasma cystatin C concentrations during the first three days of CKRT are associated with early kidney function recovery.