Assessment of glomerular filtration rate by serum cystatin C in patients undergoing coronary artery bypass grafting

BACKGROUND: Assessment of renal function in patients undergoing coronary artery bypass grafting (CABG) is important. Cystatin C has been proposed as an improved indicator of renal function. The aim of this study was to assess cystatin C as an early marker of changes in glomerular filtration rate (GFR) after CABG. METHODS: Blood samples were collected from 61 CABG patients at different time points. Using (51)Cr-ethylenediaminetetraacetic acid ((51)Cr-EDTA) clearance as a 'gold standard', we compared the correlations and non-parametric receiver operator characteristic curves of serum cystatin C, serum creatinine and 24 h creatinine clearance (Ccr). RESULTS: The inverse of cystatin C correlated better with (51)Cr-EDTA than those of serum creatinine and Ccr (r = 0.8578, 0.6771 and 0.6929, respectively). Cystatin C exhibited significantly superior diagnostic accuracy for detecting GFR <80 mL/min/1.73 m(2) compared with serum creatinine (P = 0.013) and Ccr (P = 0.025); for detecting GFR <60 mL/min/1.73 m(2), cystatin C had similar diagnostic accuracy to Ccr (P = 0.812) but was superior to creatinine (P = 0.033). At the best cut-off value, cystatin C had sensitivity 89% and specificity 93% for detecting GFR <80 mL/min/1.73 m(2), sensitivity 86% and specificity 96% for detecting GFR <60 mL/min/1.73 m(2). CONCLUSIONS: Cystatin C is a better marker for detecting small temporary changes of GFR in CABG patients. This may allow better identification of patients with renal impairment.