Factors Other than GFR Affecting Serum Cystatin C Levels

By L. Stevens, Christopher H. Schmid, Tom Greene, Liang Li, G. Beck, M. Joffe, M. Froissart, J. Kusek, Y. Zhang, Josef Coresh and 1 more. Kidney International, 2008

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Cystatin C is gaining acceptance as an endogenous filtration marker. Factors other than glomerular filtration rate (GFR) that affect the serum level have not been carefully studied. In a cross-sectional analysis of a pooled dataset of participants from clinical trials and a clinical population with chronic kidney disease (N=3418), we related serum levels of cystatin C and creatinine to clinical and biochemical variables after adjustment for GFR using errors-in-variables models to account for GFR measurement error. GFR was measured as urinary clearance of 125I-iothalamate and 15Cr-EDTA. Cystatin C was assayed at a single laboratory and creatinine was standardized to reference methods. Mean (SD) creatinine and cystatin C were 2.1 (1.1) mg/dL and 1.8 (0.8) mg/L, respectively. After adjustment for GFR, cystatin C was 4.3% lower for every 20 years of age, 9.2% lower for female sex but only 1.9% lower in blacks. Diabetes was associated with 8.5% higher levels of cystatin C and 3.9% lower levels of creatinine. Higher C-reactive protein and white blood cell count and lower serum albumin were associated with higher levels of cystatin C and lower levels of creatinine. Adjustment for age, sex and race had a greater effect on association of factors with creatinine than cystatin C. In conclusion, cystatin C is affected by factors other than GFR. Clinicians should consider these factors when interpreting the serum levels or GFR estimates from cystatin C.

Subfields: Nephrology, Pediatrics, Perinatology and Child Health

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