REFERENCE INTERVALS FOR THE GLOMERULAR-FILTRATION RATE AND CELL-PROLIFERATION MARKERS - SERUM CYSTATIN-C AND SERUM BETA(2)MICROGLOBULIN CYSTATIN-C-RATIO/

Recent studies have indicated that serum and plasma cystatin C are bet ter markers for glomerular filtration rate (GFR) than serum creatinine , ubiquitously used for this purpose. To fully exploit the value of se rum and plasma cystatin C as GFR markers, reliable age and sex-correla ted reference intervals are required. The present study comprised cyst atin C determinations in plasma and sera from 259 individuals from a w ell-defined area in the southernmost part of Sweden. From demographic lists two men and two women were randomly selected from each one-year birth cohort above 20 years of age. No sex differences were found for plasma and serum cystatin C, whereas an increase in the cystatin C lev els with age was noted, corresponding to the known age-related decreas e in GFR. The following reference intervals are recommended for practi cal clinical use: S-Cystatin C (both sexes): 20-50 years, 0.70-1.21 mg l(-1) and 50+ years, 0.84-1.55 mg l(-1). The same samples were also u sed for determination of beta(2)-microglobulin levels in order to calc ulate reference intervals for the beta(2)-microglobulin/cystatin C-rat io, which is a more distinct marker for cell proliferation, particular ly lymphoproliferation, than is the serum level of beta(2)-microglobul in alone, since the ratio should be virtually uninfluenced by GFR. The beta(2)-microglobulin/cystatin C-ratios were uninfluenced by sex and age and 1.45-2.43 is recommended as the serum reference interval for p ractical clinical use. Serum creatinine was determined in the same sam ples and the creatinine level was found to be strongly influenced by s ex and weakly by age.