Defining the relationship between average glucose and HbA1c in patients with type 2 diabetes and chronic kidney disease

Aims: To examine the relationship between average glucose (AG) and HbA1c in patients with and without chronic kidney disease (CKD) and type 2 diabetes. Materials and methods: 43 patients with diabetes and CKD (stages 3-5) with stable glycaemic control, and glucose-lowering and erythropoiesis stimulating agent (ESA) doses, were prospectively studied for 3 months and compared to 104 age-matched controls with diabetes, without CKD from the ADAG study. Over 3 months, AG was calculated from 7 to 8 point self-monitored blood glucose measurements (SMBG) and from continuous glucose monitoring (CGMS), and mean HbA1c was calculated from 4 measurements. AG and HbA1c relationships were determined using multivariable linear regression analyses. Results: The CKD and non-CKD groups were well matched for age and gender. Mean AG tended to be higher (p = 0.08) but HbA1c levels were similar (p = 0.68) in the CKD compared with non-CKD groups. 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, all p <0.01). The inclusion of ESA use in the model rendered the effect of CKD stage insignificant (R2 = 0.67, p <0.01). Conclusions: In patients with type 2 diabetes and CKD there is a linear relationship between HbA1c and AG that is attenuated by ESA use, suggesting that ESA results in a systematic underestimation of AG derived from HbA1c.