No association between hemoglobin A1c and in-hospital mortality in patients with diabetes and acute myocardial infarction

Background Patients with diabetes have increased in-hospital mortality following acute myocardial infarction (AMI), with studies suggesting higher risk with both hypoglycemia and hyperglycemia. We assessed whether a J-shaped relation exists between hemoglobin A1c (A1C) in patients with diabetes and AMI. Methods We assessed the associations between A1C and in-hospital mortality using data from a nationwide sample of AMI patients who had both prior diabetes and measurement of A1C (N = 15,337). Results When evaluated continuously, we observed no evidence of a J-shaped relation between A1C and in-hospital mortality in multivariable analysis (test for linearity P=.89). Patients with lowest (<5.5%) and highest A1C (>= 9.5%) had a crude mortality rate of 4.6% and 2.8%, respectively, compared with 3.8% among those in the referent A1C category (6.5% to <7%). In multivariable regression, we observed no association between low A1C (<5.5%, odds ratio 0.81, 95% CI 0.47-1.39) or high A1C (A1C >= 9.5, odds ratio 1.31, 95% CI 0.94-1.83) and mortality as compared with the referent group. These findings can only be generalized to the subset of patients with diabetes who had A1C assessed during their hospitalization; these patients tended to be healthier than those in whom A1C was not assessed. Conclusion In this large contemporary cohort of patients with diabetes presenting with AMI, we did not observe a J-shaped association between A1C and mortality. (Am Heart J 2011; 161: 657-663.e1.)