No Association Between Hemoglobin A1c and In-Hospital Mortality in Patients With Diabetes and Acute Myocardial Infarction

Study Questions:

What is the relationship between hemoglobin A1c (A1C) and in-hospital mortality among patients with diabetes and acute myocardial infarction (AMI)?


The investigators assessed the associations between A1C and in-hospital mortality using data from a nationwide sample of AMI patients, captured in the NCDR┬« ACTION Registry┬«-GWTG™, who had both prior diabetes and measurement of A1C (n = 15,337). The relationship between A1C and in-hospital mortality was assessed using the logistic generalized estimating equations method with exchangeable working correlation matrix to account for within-hospital clustering because patients at the same hospital are more likely to be similar and have similar responses relative to patients at other hospitals (i.e., within-center correlation for responses).


When evaluated continuously, the investigators observed no evidence of a J-shaped relation between A1C and in-hospital mortality in multivariable analysis (test for linearity, p = 0.89). 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, there was no association between low A1C (<5.5%; odds ratio, 0.81; 95% confidence interval [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.


The authors concluded that in a large contemporary cohort of patients with diabetes presenting with AMI, they did not observe a J-shaped association between A1C and mortality.


In this study, there was no evidence for a J-shaped relationship between A1C and mortality in patients with diabetes presenting with AMI. Specifically, there was no association between low A1C and in-hospital mortality even in analyses restricted to patients receiving pharmacologic therapy for diabetes. There was, however, a modest association between increasing A1C and mortality when analyzing A1C as a continuous variable. Overall, these findings are consistent with glucose serving as a risk marker and low A1C, which reflects the fact that longer-term low glucose levels should not be associated with increased mortality if glucose is primarily serving as a marker of acute illness severity.

Keywords: Hemoglobin A, Glycosylated, Myocardial Infarction, Hospital Mortality, Diabetes Mellitus, Glucose

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