PT - JOURNAL ARTICLE AU - Tan, G.D. AU - Lewis, A.V. AU - James, T.J. AU - Altmann, P. AU - Taylor, R.P. AU - Levy, J.C. TI - Clinical Usefulness of Cystatin C for the Estimation of Glomerular Filtration Rate in Type 1 Diabetes AID - 10.2337/diacare.25.11.2004 DP - 2002 Nov 01 TA - Diabetes Care PG - 2004--2009 VI - 25 IP - 11 4099 - http://care.diabetesjournals.org/content/25/11/2004.short 4100 - http://care.diabetesjournals.org/content/25/11/2004.full SO - Diabetes Care2002 Nov 01; 25 AB - 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.