A1C and Cardiovascular Outcomes in Type 2 Diabetes: A nested case-control study

OBJECTIVE: Type 2 diabetes is associated with increased cardiovascular risk. The role of aggressive glycemic control in preventing cardiovascular events is unclear. A nested case-control study design was used to evaluate the association between average A1C and cardiovascular outcomes. RESEARCH DESIGN AND METHODS: Adults with type 2 diabetes were identified among members of Kaiser Permanente Southern California. Type 2 diabetes was identified based on ICD-9 diagnosis codes and either A1C >7.5% or prescriptions for hypoglycemic agents. Case subjects were defined based on nonfatal myocardial infarction, nonfatal stroke, or death attributed to cardiovascular events during a 3-year window. Four type 2 diabetes control subjects were matched to each case subject based on age, sex, and index date for the corresponding case. A conditional logistic regression model was used to estimate the odds ratio of cardiovascular events and compare three patient groups based on average A1C measured in the preindex period (≤6, >6–8, >8%). RESULTS: A total of 44,628 control subjects were matched to 11,157 case subjects. Patients with an average A1C ≤6% were 20% more likely to experience a cardiovascular event than the group with an average A1C of >6–8% (P < 0.0001). Patients with an average A1C >8% experienced a 16% increase in the likelihood of a cardiovascular event (P < 0.0001). We found evidence of statistical interaction with A1C category and LDL level (P = 0.0002), use of cardiovascular medications (P = 0.02), and use of antipsychotics (P = 0.001). CONCLUSIONS: High-risk patients with type 2 diabetes who achieved mean A1C levels of ≤6% or failed to decrease their A1C to <8% are at increased risk for cardiovascular events.