Contemporary Risk Estimates of Three HbA1c Variables for Myocardial Infarction in 101,799 Patients Following Diagnosis of Type 2 Diabetes

OBJECTIVE: This study evaluated the risk of myocardial infarction (MI) by impaired glycemic control in a contemporary large cohort of patients with type 2 diabetes followed from diagnosis. RESEARCH DESIGN AND METHODS: Patients with type 2 diabetes diagnosed between 1995 and 2011 were retrieved from the Clinical Practice Research Datalink in the U.K., and followed from diagnosis until event of MI or end of study in 2013. Two subcohorts were defined: an early cohort with those diagnosed from 1997 to 2004 and a recent cohort with those diagnosed from 2004 to 2011. Association between each of three HbA1c metrics and MI was estimated using adjusted proportional hazards models. RESULTS: In the overall cohort (n = 101,799), the risk increase for MI per 1% (10 mmol/mol) increase in HbA(1c) was higher for updated latest and updated mean HbA(1c) of 1.11 (95% CI 1.09-1.13) and 1.15 (1.13-1.18) than for baseline HbA(1c) of 1.05 (1.03-1.06). In the early subcohort, the corresponding risk estimates were greater than those in the recent subcohort. When categorized, the updated latest variable showed an increased risk for HbA(1c) <6% (42 mmol/mol), relative category 6-7%, in the recent but not in the early subcohort, with hazard ratios of 1.23 (1.08-1.40) and 1.01 (0.84-1.22), respectively. CONCLUSIONS: The two time-updated HbA(1c) variables show a stronger relation with MI than baseline HbA(1c). The risk association between HbA(1c) and MI has decreased over time. In recently diagnosed patients with type 2 diabetes, an increased risk of MI exists at a current HbA(1c) of <6.0% (42 mmol/mol).