title: Clinical usefulness of cystatin C for the estimation of glomerular filtration rate in type 1 diabetes: reproducibility and accuracy compared with standard measures and iohexol clearance.
abstract: OBJECTIVE-Assessment and follow-up of early renal dysfunction is important in diabetic nephropathy. Plasma creatinine is insensitive for a glomerular filtration rate (GFR) >50 ml/min and creatinine clearance is unwieldy and subject to collection inaccuracies. We aimed to assess the reproducibility, reliability, and accuracy of plasma cystatin C as a measure of GFR ranging from normal to moderate impairment due to type 1 diabetes in the presence of a normal plasma creatinine concentration. RESEARCH DESIGN AND METHODS-A sensitive immunoturbidimetric cystatin C assay was examined in 29 subjects with type 1 diabetes and 11 nondiabetic subjects. Duplicate measurements of the following were collected from each subject, 2 weeks apart: cystatin C, enzymatic plasma creatinine, 24-h creatinine clearance, GFR estimated from plasma creatinine by the Cockcroft-Gault equation, and iohexol clearance as a gold standard. RESULTS-Iohexol clearance ranged from 35 to 132 ml. min(-1). 1.73 m(-2). Plasma cystatin C compared well with the other clinically used tests. The reliability of cystatin C, as assessed by the discriminant ratio, was superior to creatinine clearance (3.4 vs. 1.5, P < 0.001) and the correlation of cystatin C with iohexol clearance (Rs -0.80) was similar to that of creatinine clearance (Rs -0.74) and superior to that of plasma creatinine and the Cockcroft-Gault estimate (Rs -0.54 and 0.66, respectively). Duplicate estimations were used to provide an unbiased equation to convert plasma cystatin C to GFR. CONCLUSIONS-Based on this study, cystatin C is a more reliable measure of GFR than creatinine clearance, is more highly correlated with iohexol clearance than plasma creatinine, and is worthy of further investigation as a clinical measure of GFR in type 1 diabetes.
authors.affiliation: Oxford Centre for Diabetes, Endocrinology & Metabolism, Oxford, U.K.
authors.forename: G D
authors.initials: GD
authors.lastname: Tan
authors.forename: A V
authors.initials: AV
authors.lastname: Lewis
authors.forename: T J
authors.initials: TJ
authors.lastname: James
authors.forename: P
authors.initials: P
authors.lastname: Altmann
authors.forename: R P
authors.initials: RP
authors.lastname: Taylor
authors.forename: J C
authors.initials: JC
authors.lastname: Levy
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D003287:Contrast Media; D003404:Creatinine / Q000378:metabolism; D055316:Cystatin C; D015891:Cystatins / Q000032:analysis*; D003922:Diabetes Mellitus, Type 1 / Q000097:blood / Q000503:physiopathology* / Q000652:urine; D005260:Female; D005919:Glomerular Filtration Rate; D006442:Glycated Hemoglobin / Q000032:analysis; D006801:Humans; D007472:Iohexol / Q000493:pharmacokinetics; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D012016:Reference Values; D012044:Regression Analysis; D015203:Reproducibility of Results
chemical_list: D015415:Biomarkers; D003287:Contrast Media; D003404:Creatinine; D055316:Cystatin C; D015891:Cystatins; D006442:Glycated Hemoglobin; D007472:Iohexol; C525030:CST3 protein, human