Clinical assessment of serum cystatin C as a marker of glomerular filtration rate in patients with various renal diseases

Background. Recent reports have raised questions about the validity of estimating glomerular function and changes in glomerular function from measurements of serum creatinine. To evaluate the clinical usefulness of serum creatinine levels in terms of estimation of glomerular filtration rate (GFR), we determined serum cystatin C levels in 152 patients with various renal diseases and compared them with serum creatinine levels. Methods. Serum cystatin C levels were measured by particle-enhanced immunonephelometry. Two-h creatinine clearance (Ccr) was used as an indicator of GFR. Results. There was a significant positive correlation between serum cystatin C and creatinine levels (r = 0.941) in patients with various renal diseases. Serum cystatin C and creatinine were inversely correlated to Ccr. The overall correlation between serum cystatin C and Ccr was slightly stronger than that between serum creatinine and Ccr. In the patient group with a critical Ccr level (Ccr, 60–80 ml/min per 1.48 m²), the correlation between the reciprocal serum cystatin C levels and Ccr (r = 0.441) was significantly stronger (P < 0.01) than that between the reciprocal serum creatinine levels and Ccr (r = 0.212). A mild reduction of Ccr was detected more easily by serum cystatin C than by serum creatinine, as the clinical sensitivity and specificity of serum cystatin C were superior to that of serum creatinine. Conclusions. The cystatin C assay by particle-enhanced immunonephelometry was found to be a sensitive, fully automated, and rapid method. Serum cystatin C appears to be a promising marker of GFR in patients with impaired renal function. Its diagnostic potential was slightly superior to that of serum creatinine in adults with various renal diseases. Received: October 7, 1998 / Accepted: November 4, 1999