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Cystatin C, Urine
Cystatin C is a small, 13 kDa, non-glycosylated basic protein belonging to the cystatin super-family of cysteine protease inhibitors. Cystatin C is produced by virtually all nucleated cells, and is present in all body fluids investigated. The production rate is constant and is unaltered in inflammatory conditions. In the normal kidney, cystatin C is almost freely filtered through the glomerular membrane and then nearly completely reabsorbed and degraded by the proximal tubular cells. Therefore, the plasma concentration of cystatin C is almost exclusively determined by the glomerular filtration rate (GFR), making Cystatin C an excellent indicator for GFR.
The cystatin C assay is a solid phase ELISA designed to measure cystatin C in cell culture supernates, serum, plasma, saliva, urine, and human milk. This assay employs the quantitative sandwich enzyme immunoassay technique.
Cystatin C is reported as a normalized ratio to urinary creatinine in order to account for variations in urine flow rate. Therefore cystatin C and urine creatinine are preferably tested from the same aliquot.
*Please contact nexelis for stability information.
- Beilby J, Divitini ML, Knuiman MW, Rossi E, Hung J. Comparison of cystatin C and creatinine as predictors of cardiovascular events in a community-based elderly population. Clin Chem. 2010; 56:799-804.