Nerve function varies with hemoglobin A1c in controls and type 2 diabetes

Aims: To determine the cross-sectional threshold at which hemoglobin A1c (HbA1c) is associated with polyneuropathy in healthy controls, and the values associated with the most pronounced decline in nerve function in patients with diabetes. Methods: We used data from a cross-sectional cohort study of healthy controls and type 2 diabetes patients assessed between November 2010 and May 2013. Healthy controls and patients with diabetes were compared at different HbA1c ranges: <5.5%, 5.5–5.9%, and 6–6.4% for controls, and 6.5–7.4% and >7.5% for patients with diabetes. Results: The total cohort included 53 controls and 164 patients with diabetes. Subclinical small nerve fiber impairments were observed in controls at HbA1c levels of 5.5–6%, compared with HbA1c <5.5%, for example: lower Laser Doppler flare imaging area of 2.8 ± 1.4 versus 3.9 ± 2 mm ² . The most prominent decline in both small and large nerve fiber function was seen with less impaired glycemic control and shorter duration of diabetes, i.e. at HbA1c levels of 6.5–7.4%, compared with >7.5%. Conclusions: These findings underscore the importance of early treatment at the prediabetes and early diabetes stages to prevent nerve fiber decline that is likely irreversible.