HbA(1c) and Risk of Severe Hypoglycemia in Type 2 Diabetes: The Diabetes and Aging Study

OBJECTIVE: We examined the association between HbA(1c) 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 HbA(1c) 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 HbA(1c) levels. We also tested whether the HbA(1c)-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 HbA(1c) 7.5 ± 1.5%), 985 (10.8%) reported experiencing severe hypoglycemia. Across HbA(1c) levels, rates of hypoglycemia were 9.3–13.8%. Compared with those with HbA(1c) 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 HbA(1c) <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 HbA(1c)-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.