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

Abstract

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.