Is glomerular filtration rate estimation in diabetes influenced by creatinine methodology

BACKGROUND: Recent evidence suggest that CKD- EPI-equation might be the most accurate tool for estimating glomerular filtration rate (eGFR) in routine evaluation and staging of chronic kidney disease (CKD) in diabetic patients. Analytical performance and specificity of serum creatinine assay are critical determinants of eGFR accuracy. The aim of this study was to evaluate possible influence of creatinine methodology on the performance of CKD-EPI-calculated eGFR for CKD evaluation and staging in diabetic patients.. METHODS: Serum creatinine was measured by both IDMS-traceable compensated Jaffe and enzymatic procedure with intra-assay imprecision (CV) of 1, 43% and 1, 39%, respectively. Assay-specific GFR was estimated by the 4-variable CKD-EPI equation using respective creatinine values, and their agreement regarding clinical CKD staging evaluated by kappa-analysis. RESULTS: A total of 391 diabetic patients [M/F: 181/210 ; age range 18-88 (median 64 years), plasma glucose range 2, 3-26, 3 (median 9, 2 mmol/L), all Caucasians] were included in this study. Passing-Bablok regression analysis revealed a small, but significant constant difference between the assays (y=2, 6667+0, 9744x) across a wide range of creatinine values (35-522 μmol/L). CKD-EPI-eGFR values, ranging from 9- 136 ml/min/1, 73m2, showed an insignificant difference depending on creatinine assay used for eGFR calculation (y=1, 000+1, 000x). Linear regression analysis identified plasma glucose as significant determinant of bias between eGFR values calculated using compensated Jaffe and enzymatic creatinine values in all patients (P 8, 0% (63, 9 mmol/mol), N=115, P<0, 001], Inter-rater agreement analysis showed excellent agreement (weighted kappa=0, 909) between the creatinine- specific-eGFRs when classifying subjects into CKD-stages. CONCLUSIONS: Results obtained from this cross- sectional study could not demonstrate any significant influence of creatinine methodology on clinical outcomes, assessed by eGFR-based CKD staging in diabetic patients. Compensated Jaffe alkaline picrate procedure may introduce only a minor variation of kidney function assessment in patients with poor glycaemic control and very early stages of CKD.