Measurement of cystatin C is an indicator of glomerular filtration rate, especially in patients where serum creatinine may be misleading, for example in very obese, elderly, and malnourished patients. Cystatin C measurement is used to evaluate renal function in patients with suspected renal disease and to monitor treatment response in patients with renal disease.
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Cystatin C is a low molecular weight cysteine protease inhibitor that is produced by all nuclear cells and is found in body fluids, including serum. Since it is formed at a constant rate and is filtered free from the kidneys, its serum concentration is inversely correlated with the glomerular filtration rate (GFR), that is, high cystatin C values indicate low GFR while lower cystatin C subunits indicate higher GFR, just as with creatinine.
The course of cystatin C in the kidneys differs from that of creatinine. While both substances are filtered free by glomeruli, after being filtered, cystatin C, unlike creatinine, is absorbed and metabolized in the proximal renal tubules. Thus, under normal conditions, cystatin C does not enter the excreted urine significantly.
The serum cystatin C concentration remains unchanged in infections, inflammatory, or neoplastic conditions and is not affected by body mass, nutrition, or medication. Thus, cystatin C may be a more reliable indicator of renal function (GFR) than creatinine.
Important Note
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.
