Determination of serum cystatin C: Biological variation and reference values

Human cystatin C is a low molecular weight protein which has been proposed as a better marker of glomerular filtration rate than creatinine. To be abl e to interpret results obtained in different patient populations it is nece ssary to define cystatin C reference values. We measured serum concentratio n of cystatin C in 1223 subjects using a particle-enhanced nephelometric as say. Subjects were aged 4 to 79 years and were selected among apparently he althy individuals who came to the Centre for Preventive Medicine in Vandoeu vre-Les-Nancy, France. We observed a Gaussian distribution of cystatin C co ncentration in serum. We did not find any effect of age or gender in childr en, hormonal status in women (puberty, menopause, oral contraceptives or ho rmone replacement therapy) or alcohol intake. Cystatin C concentration was slightly lower in female than in male adults below the age of 60 years. Cys tatin C levels significantly increased above the age of 60 in both males an d females, probably due to physiological aging of renal function. No other significant differences were observed between males and females. Using mult iple regression analysis, moderate correlations were observed between body mass index and cystatin C, and between smoking and cystatin C, but these we re not biologically significant. According to the literature, only methylpr ednisolone and cyclosporin A increased and decreased cystatin C levels, res pectively. The reference values for cystatin C obtained in a carefully sele cted population were 0.75 +/- 0.089 mg/l for children aged 4-19 years, 0.74 +/- 0.100 mg/l for males and 0.65 +/- 0.085 mg/l for females (aged 20-59 y ears), and 0.83 +/- 0.103 mg/l for older individuals (greater than or equal to 60 years).