Longitudinal Mean HbA1c and Electrodiagnostic Severity of Distal Symmetric Sensorimotor Polyneuropathy in Type 2 Diabetes: Comparison With Index HbA1c

Objective: To evaluate the association of longitudinal mean glycosylated hemoglobin (HbA1c) with electrodiagnostic severity of distal symmetric sensorimotor polyneuropathy (DSPN), using index HbA1c as a comparator.Methods: We retrospectively reviewed patients with type 2 diabetes undergoing nerve conduction studies (NCS) during 2022–2024. Eligibility required ≥4 HbA1c measurements spanning ≥2 calendar years within a capped 4-year look-back window including the NCS month. Mean HbA1c averaged these measurements; index HbA1c was the measurement closest to NCS within ±3 months. The primary outcome was ordinal Baba stage (0–4). Separate ordinal models used parsimonious and full covariate adjustment. Paired bootstrap resampling and joint models directly compared associations. Exploratory paired receiver operating characteristic analyses assessed advanced electrodiagnostic DSPN (Baba stages 3–4). Penalized analyses assessed stability; additional analyses evaluated time-weighted means and HbA1c coefficient of variation (CV).Results: Of 263 screened patients, 73 were included. Mean HbA1c correlated with Baba stage (ρ=0.320, p=0.006). Fully adjusted odds ratios were 1.51 for mean HbA1c (95% confidence interval [CI], 1.03–2.22) and 1.31 for index HbA1c (95% CI, 0.98–1.76). The paired bootstrap 95% CI for the difference in log-odds ratios included zero (-0.152 to 0.650). Mean HbA1c remained associated with advanced DSPN; areas under the curve were 0.701 and 0.618, respectively (DeLong p=0.153), with an exploratory threshold of 7.0%. Ordinal associations were attenuated with time-weighted means or CV adjustment.Conclusion: Mean HbA1c showed more consistent associations than index HbA1c across separate models, but superiority was not established. Sensitivity analyses indicated uncertainty in the ordinal association.