Early postoperative serum cystatin C predicts severe acute kidney injury following cardiac surgery: a post-hoc analysis of a randomized controlled trial

OBJECTIVE Acute kidney injury (AKI) after cardiac surgery procedures is associated with poor patient outcomes. Cystatin C as a marker for renal failure has been shown to be of prognostic value; however, a wide range of its predictive accuracy has been reported. The aim of the study was to evaluate whether the measurement of pre- and postoperative serum cystatin C improves the prediction of AKI. METHODS In a single-centre, prospective study of 70 patients (74 ± 9 ys; range 47-85 ys; 77% male), cystatin C was measured six times: (T1=preoperative, T2=start cardiopulmonary bypass (CPB), T3=20 min after CPB, T4=end of operation; T5=24 h postoperatively; T6=7d postoperatively). Predictive property, in terms of the need for renal replacement therapy (RRT), was analysed by receiver operating characteristics (ROC) statistics and described by the area under the curve (AUC). RESULTS With respect to RRT (n=8), serum cystatin C was significantly higher at the end of the operation (T4), 24 h postoperatively at T5 and at T6. The AUCs for preoperative T1 and intraoperative T2/3 cystatin C were <0.7 (95% CI, 0.47-0.85). The earliest significant predictive AUCs were found at the end of the operation (T4: p=0.03 95% CI 0.58-0.88 AUC 0.73) and 24 h postoperatively (T5: p=0.003 95% CI 0.74-0.96 AUC 0.85). CONCLUSIONS Early postoperative serum cystatin C increase appears to be a moderate biomarker in the prediction of AKI, whereas a preoperative and intraoperative cystatin C increase has only a limited diagnostic and predictive value.