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.