Reference Intervals and Factors Contributing to Serum Cystatin C Levels in a Chinese Population

Background: Serum cystatin C (Cys-C), an inhibitor of cysteine proteases, has been suggested as an ideal biomarker of glomerular filtration rate (GFR). Objectives: The objective of this study was to describe the reference intervals of serum CysC and identify factors associated with serum Cys-C or its variability, including age, gender, creatinine (Crea), blood urea nitrogen (BUN), and uric acid (UA). Design and Methods: Serum Cys-C, Crea, BUN, and UA were measured in 4,517 healthy participants aged 8-89 years attending our hospital. Serum Cys-C was analyzed using a latex-enhanced immunoturbidimetric method. Crea were tested by picric acid jaffe method, BUN, and UA by kinetic UV assays. Results: The predominant characteristic of Cys-C distribution was that Cys-C concentration in age >= 60 years group was the highest (P < 0.05). The differences of Cys-C concentration between males and females existed for subjects aged from 30 to 59 years (P < 0.05). In a multiple model adjusted only for gender and age, gender (beta = 0.007) has stronger effect on Cys-C levels, compared with age (beta = 0.003). The clinical variables, comprised of age, gender, Crea, BUN, and UA, involved in the fully adjusted equation accounted for 37.6% of variation of Cys-C. Conclusions: Ninety-five percent reference intervals for healthy population were partitioned into three categories only by age, 0.59-1.07 mg/L for subjects aged 19-59 years; 0.74-1.14 mg/L for the older aged >= 60 years; and 0.63-1.11 mg/L for children aged <= 18 years. Serum Cys-C is significantly related to gender, age, UA, Crea, and BUN. Besides, there are still other factors contributing to variation of CysC levels. J. Clin. Lab. Anal. 26:49-54, 2012. (C) 2012 Wiley Periodicals, Inc.