Cystatin C is not more sensitive than creatinine for detecting early renal impairment in patients with diabetes

Abstract

This study evaluated serum cystatin C as a potential new marker of glomerular filtration rate (GFR) in 49 patients who had steady-state diabetes with early renal impairment. We determined the correlation between GFR measured by chromium 51-labeled EDTA and levels of serum cystatin C, serum creatinine, serum [beta ]2-microglobulin, endogenous creatinine clearance, and Cockcroft formula. Sensitivity and specificity for the diagnosis of renal failure, defined as a GFR less than either 80 or 60 mL/min/1.73 m2, were calculated by receiver operating characteristic (ROC) curves for creatinine, cystatin C, and [beta ]2-microglobulin. Finally, we compared mean values of these three serum parameters in patients grouped according to GFR using the two definitions of renal failure. Correlation coefficients with GFR were [minus ]0.77 for serum creatinine level, [minus ]0.65 for serum cystatin C level, [minus ]0.71 for serum [beta ]2-microglobulin level, +0.56 for endogenous creatinine clearance, and +0.69 for Cockcroft formula (all P [lt ] 0.001). With a cutoff value of 60 mL/min/1.73 m2, areas under the ROC curve were 0.972 for [beta ]2-microglobulin, 0.925 for cystatin C, and 0.916 for creatinine levels. With a cutoff value of 80 mL/min/1.73 m2, these were 0.838 for [beta ]2-microglobulin, 0.780 for cystatin C, and 0.905 for creatinine levels (P [equals] not significant between parameters). These results were not altered after the exclusion of patients (n [equals] 8) with a serum creatinine level greater than 1.41 mg/dL. When patients were classified into three groups according to GFR (group 1, [gt ]80 mL/min/1.73 m2; group 2, 60 to 80 mL/min/1.73 m2; group 3, [lt ]60 mL/min/1.73 m2), mean values of serum parameters in the three groups were statistically different (P [lt ] 0.0001) except between groups 1 and 2 for cystatin C and [beta ]2-microglobulin. With patients classified into two groups (GFR [gt ] or [lt ] 80 mL/min/1.73 m2), mean values for each parameter were statistically different (P [lt ] 0.001). Sensitivity, specificity, and positive and negative predictive values for serum creatinine and serum cystatin C levels were very close for both definitions of renal failure. Serum cystatin C is not better than serum creatinine or serum [beta ]2-microglobulin levels for estimating GFR in patients with steady-state diabetes using ROC curves or other validation tests. [copy ] 2001 by the National Kidney Foundation, Inc.