BETTER TEST for CKD

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Cystatin C May Trump Creatinine in Determining CKD Risk

Larry Hand
Sep 09, 2013



 

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Cystatin C alone, or in combination with, creatinine may be a better predictor for death or renal disease than creatinine alone, researchers report in an article published in the September 5 issue of the New England Journal of Medicine. Use of cystatin C may also help physicians better identify patients with chronic kidney disease (CKD) who need intense monitoring or treatment, according to the study results.
 
The study follows the development of an international cystatin C reference standard for use in various laboratories and publication by the Chronic Kidney Disease Epidemiology Collaboration of improved equations to determine an estimated glomerular filtration rate (eGFR).

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Kidney function[edit source]
 
Glomerular filtration rate (GFR), a marker of kidney health, is best measured by injecting compounds such as inulin, radioisotopes such as 51chromium-EDTA, 125I-iothalamate, 99mTc-DTPA or radiocontrast agents such as iohexol, but these techniques are complicated, costly, time-consuming and have potential side-effects.[2][3] Creatinine is the most widely used biomarker of kidney function. It is inaccurate at detecting mild renal impairment, and levels can vary with muscle mass and protein intake.[4] Formulas such as the Cockcroft and Gault formula and the MDRD formula (see Renal function) try to adjust for these variables.
 
Cystatin C has a low molecular weight (approximately 13.3 kilodaltons), and it is removed from the bloodstream by glomerular filtration in the kidneys. If kidney function and glomerular filtration rate decline, the blood levels of cystatin C rise. Serum levels of cystatin C are a more precise test of kidney function (as represented by the glomerular filtration rate, GFR) than serum creatinine levels.[3][5] This finding is based mainly on cross-sectional studies (on a single point in time). Longitudinal studies (that follow cystatin C over time) are scarcer; some studies show promising results.[6][7][8] Cystatin C levels are less dependent on age, sex, race and muscle mass compared to creatinine. Cystatin C measurements alone have not been shown to be superior to formula-adjusted estimations of kidney function.[9] As opposed to previous claims, cystatin C has been found to be influenced by body composition.[10][11] It has been suggested that cystatin C might predict the risk of developing chronic kidney disease, thereby signaling a state of 'preclinical' kidney dysfunction.[12]
 
Studies have also investigated cystatin C as a marker of kidney function in the adjustment of medication dosages.[13][14]
 
Cystatin C levels have been reported to be altered in patients with cancer,[15][16