title: Factors other than glomerular filtration rate affect serum cystatin C levels.
abstract: Cystatin C is an endogenous glomerular filtration marker hence its serum level is affected by the glomerular filtration rate (GFR). To study what other factors might affect it blood level we performed a cross-sectional analysis of 3418 patients which included a pooled dataset of clinical trial participants and a clinical population with chronic kidney disease. The serum cystatin C and creatinine levels were related to clinical and biochemical parameters and errors-in-variables models were used to account for errors in GFR measurements. The GFR was measured as the urinary clearance of 125I-iothalamate and 51Cr-EDTA. Cystatin C was determined at a single laboratory while creatinine was standardized to reference methods and these 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 gender 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, gender and race had a greater effect on the association of factors with creatinine than cystatin C. Hence, we found that cystatin C is affected by factors other than GFR which should be considered when the GFR is estimated using serum levels of cystatin C.
authors.affiliation: Division of Nephrology, Clinical Care Research, Tufts Medical Center, Boston, Massachusetts 02111, USA. lstevens1@tuftsmedicalcenter.org
authors.forename: Lesley A
authors.initials: LA
authors.lastname: Stevens
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Schmid
authors.forename: Tom
authors.initials: T
authors.lastname: Greene
authors.forename: Liang
authors.initials: L
authors.lastname: Li
authors.forename: Gerald J
authors.initials: GJ
authors.lastname: Beck
authors.forename: Marshall M
authors.initials: MM
authors.lastname: Joffe
authors.forename: Marc
authors.initials: M
authors.lastname: Froissart
authors.forename: John W
authors.initials: JW
authors.lastname: Kusek
authors.forename: Yaping Lucy
authors.initials: YL
authors.lastname: Zhang
authors.forename: Josef
authors.initials: J
authors.lastname: Coresh
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Levey
mesh_terms: D000367:Age Factors; D003404:Creatinine / Q000097:blood*; D003430:Cross-Sectional Studies; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007677:Kidney Function Tests / Q000379:methods; D008297:Male; D011237:Predictive Value of Tests; D044469:Racial Groups; D012737:Sex Factors
chemical_list: D055316:Cystatin C; D003404:Creatinine