Cystatin C as a Marker for Early Renal Impairment

Background : In recent years, cystatin C was proposed as a new marker for the glomerular filtration rate due to a constant serum level, with no secretion from the renal tubule, and elimination only by the kidneys. The aim of this study was to evaluate cystatin C as a renal marker compared with creatinine. Methods : The concentration of serum creatinine, cystatin C, and creatinine clearance were measured in 119 healthy adults and 112 patients with several nephropathies. Results : The reference interval of cystatin C was 0.45-0.96 mg/L and there were no significant correlations to age, sex and bodysurface area (P>0.05). Cystatin C and creatinine were highly correlated with the glomerular filtration rate measured by creatinine clearance (r=0.810, 0.806, respectively). Diagnostic accuracy by receiver- operation characteristic curves were similar (area under the curve, cystatin C 0.853 vs. creatinine 0.882). But cystatin C showed greater sensitivity for detecting a decreased glomerular filtration rate than did creatinine (82%, 76% respectively). Especially, the sensitivity of cystatin C was higher than that of creatinine in mildly decreased groups when patients were classified into four groups according to the decrement of the glomerular filtration rate. Conclusions : Serum cystatin C is as useful as serum creatinine as a renal marker and is superior as a screening marker in detecting early renal impairment.