Background: Patients with increased glycated hemoglobin (HbA1c) seem to be at increased risk of sternal wound infection (SWI) after coronary artery bypass grafting (CABG). However, it is unclear whether increased baseline HbA1c levels may affect other postoperative outcomes.

Material and methods: Data on preoperative levels of HbA1c were collected from 2606 patients undergoing elective isolated CABG from 2015 to 2016 and included in the prospective, multicenter E-CABG registry.

Results: The prevalence of HbA1c ≥ 53 mmol/mol (7.0%) among non-diabetics was 5.3%, among non-insulin dependent diabetics was 53.5% and among insulin dependent diabetics was 67.1% (p < 0.001). The prevalence of HbA1c > 75 mmol/mol (9.0%) among non-diabetics was 0.5%, among non-insulin dependent diabetics was 5.8% and among insulin dependent diabetics was 10.6% (p < 0.001). Baseline levels of HbA1c ≥ 53 mmol/mol (7.0%) was a significant predictor of any SWI (10.7% vs. 3.3%, adjusted p-value: <0.001), deep SWI/mediastinitis (3.8% vs. 1.3%, adjusted p-value: 0.001) and acute kidney injury (27.4% vs. 19.8%, adjusted p-value: 0.042). These findings were confirmed in multilevel mixed effect logistic regression adjusted for participating centers. Among patients with diabetes, HbA1c ≥ 53 mmol/mol (7.0%) was predictive of SWI (11.1% vs. 4.8%, p = 0.001).

Conclusions: HbA1c is increased in a significant proportion of patients undergoing elective CABG and these patients are at higher risk of SWI. Less clear is the impact of increased HbA1c on other postoperative outcomes. These results do not support screening of HbA1c in patients without history of diabetes. Preoperative screening of HbA1c is valuable only to identify diabetics at risk of SWI.