Serum Cystatin C as a predictor of cardiac surgery associated-acute kidney injury in patients with normal preoperative renal functions. A prospective cohort study

Cardiac surgery-associated acute kidney injury (CSA-AKI) remains a known complication, where postoperative (PO) Cystatin C (Cys C) has been shown to be an earlier marker than the relatively late appearing creatinine (Cr). We sought to evaluate the reliability of preoperative (pre-OP) Cys C as a predictor for CSA-AKI in patients with normal renal functions. Our study included consecutive patients undergoing on-pump cardiac surgery from July 2011 to April 2012. Pre-OP and PO Cystatin C and renal profiles were compared in AKI (GP I) and non-AKI (GP II) patients. RIFLE and AKIN criteria were calculated at baseline and daily during the successive three PO days. Out of 40 patients (16 males; mean age = 59 years), 20 developed AKI. Both Pre-and PO Cys C were significantly higher in GP I, and positively correlated with PO Cr. (r: 0.38 P; 0.01; r: 0.68, p 0.04 respectively). Using ROC curve, a cutoff value of 1.8 mg/l and 1.88 (sensitivity 50 and 80%; specificity 90 and 65%) for Pre-OP and PO Cys C respectively in predicting AKI. Multivariate analysis showed the Pre-OP Cys C and cardiopulmonary bypass time were independent predictors for AKI. In patients with apparently normal renal functions, preoperative Cys C may be a predictor of post cardiac surgery AKI. In those patients, especially diabetics, Cys C may uncover subtle nephropathy which makes them more prone to AKI posed by stresses of cardiac surgery.