Comparison of cystatinC- and creatinine-based estimation of glomerular filtration rate according to glycaemic status in Type2 diabetes

Aims The influence of hyperglycaemia on the performance of glomerular filtration rate (GFR) estimating equations remains to be determined. We compared the performance of creatinine-based GFR with cystatinC-based GFR in patients with Type2 diabetes according to glycaemic status. Methods In a cross-sectional study of 210 patients with Type2 diabetes, we staged glycaemic status by HbA _1c tertiles [HbA _1c≤75mmol/mol (9.0%) (n=70), HbA _1c 76-95mmol/mol (9.1-10.8%) (n=70), HbA _1c >95mmol/mol (10.8%) (n=70)] and measured GFR. Isotopic GFR was measured using renal dynamic imaging with ^99mTc-diethylene-triamine-penta-acetic acid. Estimated GFR (eGFR) was measured using creatinine-based formulae (Cockcroft-Gault-eGFR, the Modification of Diet in Renal Disease equation-eGFR and the Chronic Kidney Disease Epidemiology Collaboration formula-eGFR) and a cystatinC-based formula (cystatinC-eGFR). Results The isotopic GFR of all patients was 93.1±34.1mlmin ^-11.73m ^-2. All methods for estimating GFR underestimated isotopic GFR [Cockcroft-Gault-eGFR (68.8±38.6mlmin ^-11.73m ^-2) (P<0.05), Modification of Diet in Renal Disease-eGFR (74.8±31.3mlmin ^-11.73m ^-2) (P<0.05), Chronic Kidney Disease Epidemiology Collaboration-eGFR (72.9±26.6mlmin ^-11.73m ^-2) (P<0.05) and cystatinC-eGFR (83.5±33.2mlmin ^-11.73m ^-2) (P<0.05)]. In all patient groups, cystatinC-eGFR was less biased and more accurate than the creatinine-based formulae, especially in the group with HbA _1c >95mmol/mol (10.8%) where there was no difference between cystatinC-eGFR and isotopic GFR. Conclusions Performance of cystatinC-eGFR was superior to creatinine-based GFR in patients with Type2 diabetes with HbA _1c >95mmol/mol (10.8%).