Serum cystatin C concentration as a marker of renal dysfunction in the elderly

Serum cystatin C is a novel marker of renal function claimed to be superior to plasma creatinine, We assessed both parameters in young normotensive su bjects (n = 12; 6 men; mean age, 25 +/- 2 years) and elderly normotensive a nd hypertensive subjects (n = 41; 19 men; mean age, 67 +/- 6 years). Glomer ular filtration rate (GFR) was measured in all individuals using the inulin clearance (C-in) technique. Compared with young subjects, mean GFR was mod estly but significantly (P < 0.001) less in elderly subjects (young, 119 +/ - 11 mL/min/1.73 m(2) versus elderly, 104 +/- 12 ml/min/1.73 m(2)). Mean pl asma creatinine concentration was identical in both groups (young, 0.93 +/- 0.11 mg/dL versus elderly, 0.93 +/- 0.10 mg/dL; P < 0.90). Mean serum cyst atin C concentration was significantly (P < 0.001) greater in elderly subje cts (0.84 +/- 0.10 mg/L) compared with young subjects (0.69 +/- 0.08 mg/L). In all butone elderly subject, plasma creatinine concentration was within the 95% confidence interval of plasma creatinine concentration in young sub jects. Eleven of 41 elderly subjects (27%) had GFRs less than the lower 95% confidence interval, respectively, ant! 12 of 41 elderly subjects (29%) ha d a serum cystatin C concentration greater than the upper 95% confidence in terval in young subjects. The correlation between serum cystatin C concentr ation and C-in (r = -0.65; P < 0.001) was considerably better;than between plasma creatinine concentration and C-in (r = -0.30; P < 0.02). Serum cysta tin C concentration is a better marker of renal dysfunction (ie, reduced GF R) than plasma creatinine concentration, at least in elderly subjects with plasma creatinine concentrations within the normal range. (C) 2001 by the N ational Kidney Foundation, Inc.