Defining the relationship between HbA1c and average plasma glucose in type 2 diabetes and chronic kidney disease.

Background and aims: Diabetic chronic kidney disease is a growing problem globally. Glycemic control is important for the prevention of adverse kidney outcomes. However, the utility of assessing HbA1c levels in patients with chronic kidney disease (CKD) remains unclear. Here we examine the relationship between average plasma glucose (AG) and HbA1c in patients with and without CKD (stages 3 to 5). Material(s) and Method(s): 43 patients with type 2 diabetes (T2DM) and CKD (33% stage 3, 23% stage 4 and 44% stage 5) with stable glycemic control, no recent changes in glucose lowering or erythropoietin therapy and no recent blood transfusions were prospectively studied and age-matched to 104 patients without CKD randomly selected from the A1c-Derived Average Glucose study. Over a 3-month period, average plasma glucose (AG) was calculated from 7-8 point self-glucose monitoring (SGM) performed 3-5 days/ week and continuous glucose monitoring (CGM) performed for 2-3 days/ month. Mean HbA1c was calculated as the average of levels measured at baseline and then monthly over 3 months. The relationship between AG (calculated separately from SGM and CGM) and HbA1c was analysed using multivariable regression models. Result(s): The CKD and non-CKD groups were well matched for age (61 +/- 4 vs. 63 +/- 9.6 years) and gender (40% vs. 37% were female). Mean AG and HbA1c levels were similar (CKD vs. non-CKD, AG: 9.1+/-2.5 vs. 8.4+/-1.9 mmol/L and HbA1c: 7.1+/-1.4 vs. 7.0+/-1.0 %, both p>0.05). A linear relationship between AG and HbA1c was observed irrespective of the presence and stage of CKD. The relationship was weaker in patients with stage 4-5 CKD (non-CKD R2 0.75, stage 3 CKD R2 0.79 and stage 4-5 CKD R2 0.34). The inclusion of erythropoietin use (EPO) into the model rendered the effect of CKD stage insignificant, suggesting that the treatment of anaemia with EPO results in a systematic underestimation of the AG derived from the HbA1c: AG (mmol/L) = 1.4(HbA1c %) + 1.1 x [EPO yes (1