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

Key Points Plasma cystatin C is decreased in participants with AKI requiring continuous KRT (CKRT) with early kidney function recovery. Despite being cleared by CKRT, plasma cystatin C in the first 3 days of CKRT may be a useful clinical tool to help predict the prognosis of AKI requiring CKRT. Background Plasma cystatin C is a reliable marker to estimate kidney function; however, it is unknown whether this remains true in patients receiving continuous KRT (CKRT). In this study, we tested the hypothesis that lower concentrations of plasma cystatin C during the first 3 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 AKI requiring CKRT: ( 1 ) with early kidney function recovery defined as liberation from KRT within 7 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 before 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 with patients with delayed kidney function recovery on days 1 (1.79 versus 2.39 mg/L), 2 (1.91 versus 2.38 mg/L), and 3 (2.04 versus 2.67 mg/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 <1.30 mg/L, and negative likelihood ratio of 0.17 for plasma cystatin C ≥1.88 mg/L. Conclusions Lower plasma cystatin C concentrations during the first 3 days of CKRT are associated with early kidney function recovery.