<![CDATA[Diabetes mellitus is a major risk factor for coronary heart disease (CHD), particularly when long-term glycemic control is inadequate. Glycated hemoglobin (HbA1c) reflects average blood glucose levels over the previous two to three months and may serve as an indicator of cardiovascular risk. This study aimed to examine the role of HbA1c levels in the incidence, severity, and clinical outcomes of CHD among patients with diabetes mellitus. A narrative literature review was conducted using articles published between 2021 and 2026 and retrieved from Google Scholar, PubMed, ScienceDirect, and ResearchGate. Studies were selected according to predetermined inclusion and exclusion criteria and critically evaluated using the Joanna Briggs Institute appraisal instruments. A total of 29 relevant studies were reviewed and synthesized narratively. Most studies demonstrated that elevated HbA1c levels were associated with an increased risk of CHD, greater coronary artery stenosis, more severe atherosclerotic lesions, and poorer cardiovascular outcomes, including major adverse cardiovascular events, restenosis following percutaneous coronary intervention, hospital readmission, and mortality. However, several cross-sectional studies reported no statistically significant association, possibly because of differences in sample characteristics, study design, duration of diabetes, assessment methods, and accompanying cardiovascular risk factors. Overall, poor glycemic control contributes to the development and progression of CHD through chronic hyperglycemia, oxidative stress, endothelial dysfunction, inflammation, and accelerated atherosclerosis. Regular HbA1c monitoring and individualized glycemic control are therefore important components of cardiovascular risk prevention and diabetes management.]]>
