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Use: Since it is formed at a constant rate and freely filtered by the healthy kidney, cystatin C is a good marker of renal function. Serum concentrations of cystatin C are almost totally dependent on glomerular filtration rate (GFR). A reduction in GFR causes a rise in the concentration of cystatin C.1,2
Can be used as a confirmatory test for the diagnosis of chronic kidney disease (CKD) in patients with a decreased GFR as estimated from creatinine.
Data suggests that 3.6% of U.S. adults would be classified as having CKD solely on the basis of a creatinine-based GFR estimate of 45 to 59 mL per minute per 1.73m2. A strategy of measuring cystatin C when the creatinine-based estimate is in this range and then reestimating GFR with the use of both these markers could correctly reclassify a substantial proportion of such patients as not having CKD and not being at high risk.
Can also be used to screen for CKD among persons who have a creatinine-based GFR estimate of 60 to 74 mL per minute per 1.73m2 without albuminuria (10.9% of US adults) or to obtain a more accurate estimation of GFR in patients with muscle wasting or chronic illness.
Limitations: Cystatin C has not been shown to be affected by factors such as muscle mass and nutrition, factors which have been demonstrated to affect creatinine values. In addition, a rise in creatinine does not become evident until the GFR has fallen by approximately 50%.
Methodology: Turbidimetric (directly traceable to ERM-DA471/IFCC, the international standard reference material)
Additional Information: The estimated glomerular filtration (GFR) provides an assessment of the filtering capacity of the kidney. The eGFR is calculated from a serum cystatin C using the CKD-EPI equation, 2012.3
