Comparison of cystatin C versus creatinine for detection of mild renal failure

Aim: Serum cystatin C (SCyst) has been proposed as a novel indicator of GFR . Patients and methods: We compared SCyst, serum creatinine (SCreat) and Co ckcroft and Gault's estimated clearance (C-CG) using inulin clearance (Cin) as gold standard. 140 subjects (161 samples; aged 39 +/- 14; male/female: 79/82) underwent simultaneous measurements. Results: A highly significant c orrelation r = 0.70, 0.74, 0.77 (p < 0.0001) was found between 1/SCyst, 1/S Creat, CCG, respectively, and Gin. Receiver-operating characteristic (ROC) analysis was performed on SCyst, SCreat and CCG using a Cin cut-off of 90 m l/min/1.73 m(2). Best fit for SCyst was 0.90 mg/l with a sensitivity of 75% and a specificity of 92%. The area under the ROC curve was not significant ly greater for SCreat or CCG than for SCyst (p = 0.91, 0.13, respectively). When relationship between Cin and SCyst was plotted, experimental data dev iated from the theoretical model, suggesting that cystatin C may not be sol ely filtered. Additional patients were selected in our database on the basi s of discordant S Creat/GFR values: false negative (n = 46 samples, 31 pati ents) and false positive (n = 16 samples, 9 patients). In this highly selec ted subgroup, 38% of the SCreat false positive had normal SCyst values and 48% of the false negative SCreat had abnormally elevated SCyst. Conclusion: This study suggests that SCyst is not more sensitive than SCreat or C-CG f or detecting renal failure, however, SCyst could be proposed as a confirmat ory test for patients with elevated SCreat.