Influence of preoperative glycosylated Hemoglobin (HbA1c) level on long-term outcomes after coronary artery bypass grafting

Background: Diabetes mellitus is highly prevalent among patients undergoing coronary artery bypass grafting (CABG), yet the prognostic significance of preoperative glycemic control remains uncertain. Thus, this study aims to investigate the association between hemoglobin A1c (HbA1c) and long-term outcomes following CABG. Methods: We conducted a retrospective cohort study of 8,147 adults who underwent isolated CABG between 2009 and 2025. Patients were included based on available HbA1c samples and categorized by preoperative HbA1c as ≤5.8%, 5.8-6.5%, or ≥6.5%. The primary outcome was all-cause mortality. Secondary outcomes included postoperative complications and intensive care unit (ICU) length of stay. Multivariable Cox proportional hazards models were used to evaluate associations between HbA1c and mortality after adjustment for demographic, clinical, and procedural factors. Subgroup analyses assessed result robustness. Results: Of the cohort, 2,630 were included with 1,022 (39%) having a HbA1c ≤5.8%, 501 (19%) 5.8-6.5%, and 1,107 (42%) ≥6.5%. Over a median follow-up of 5.2 years, mortality increased across HbA1c categories. After adjustment, HbA1c ≥6.5% was independently associated with higher mortality (HR 1.74; 95% CI 1.43-2.11; p<0.001), whereas intermediate HbA1c was not (HR 0.97; 95% CI 0.74-1.27; p=0.82). Elevated HbA1c was also associated with longer ICU stay and higher rates of sternal wound infection. Findings were consistent across age, sex, and body mass index subgroups. Conclusions: Poor preoperative glycemic control is independently associated with increased long-term mortality and postoperative morbidity after CABG. HbA1c provides important prognostic information and may inform perioperative risk stratification in patients undergoing surgical revascularization.