HbA1c and Risk of Severe Hypoglycemia in Type 2 Diabetes

OBJECTIVE We examined the association between HbA1c level and self-reported severe hypoglycemia in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS Type 2 diabetic patients in a large, integrated healthcare system, who were 30-77 years of age and treated with glucose-lowering therapy, were asked about severe hypoglycemia requiring assistance in the year prior to the Diabetes Study of Northern California survey conducted in 2005-2006 (62% response rate). The main exposure of interest was the last HbA1c level collected in the year preceding the observation period. Poisson regression models adjusted for selected demographic and clinical variables were specified to evaluate the relative risk (RR) of severe hypoglycemia across HbA1c levels. We also tested whether the HbA1c-hypoglycemia association differed across potential effect modifiers (age, diabetes duration, and category of diabetes medication). RESULTS Among 9,094 eligible survey respondents (mean age 59.5 ± 9.8 years, mean HbA1c 7.5 ± 1.5%), 985 (10.8%) reported experiencing severe hypoglycemia. Across HbA1c levels, rates of hypoglycemia were 9.3-13.8%. Compared with those with HbA1c of 7-7.9%, the RR of hypoglycemia was 1.25 (95% CI 0.99-1.57), 1.01 (0.87-1.18), 0.99 (0.82-1.20), and 1.16 (0.97-1.38) among those with HbA1c <6, 6-6.9, 8-8.9, and ≥9%, respectively, in a fully adjusted model. Age, diabetes duration, and category of diabetes medication did not significantly modify the HbA1c-hypoglycemia relationship. CONCLUSIONS Severe hypoglycemia was common among patients with type 2 diabetes across all levels of glycemic control. Risk tended to be higher in patients with either near-normal glycemia or very poor glycemic control.