Testing for HbA1c, in addition to the oral glucose tolerance test, in screening for abnormal glucose regulation helps to reveal patients with early β-cell function impairment

Background: The oral glucose tolerance test (OGTT) is recommended to screen for diabetes in patients with coronary artery disease. We hypothesized that testing for glycated hemoglobin (HbA(1c)), in addition to the OGTT, in screening for abnormal glucose regulation may help to reveal patients with beta-cell function impairment. Methods: Patients with no history of diabetes who were admitted for coronary angiography were recruited to undergo an OGTT and HbA(1c) test 2-4 weeks after hospital discharge. beta-cell function and insulin resistance were assessed using the homeostasis model assessment (HOMA-beta and HOMA-IR, respectively). For patients with normal glucose tolerance (NGT) based on the OGTT, we compared HOMA-beta between two subgroups of patients using an HbA(1c) cutoff of 39 mmol/mol or 42 mmol/mol. For patients with prediabetes based on an OGTT, we compared the HOMA-beta between two subgroups of patients using an HbA(1c) cutoff of 48 mmol/mol. Results: A total of 1044 patients were analyzed. In patients with NGT by OGTT (n = 432), those with an HbA(1c) = 42 mmol/mol had a lower HOMA-beta compared to those with an HbA(1c) <42 mmol/mol (107 +/- 82 vs. 132 +/- 96, p = 0.018). In patients with prediabetes by OGTT (n = 423), those with an HbA(1c) = 48 mmol/mol had a lower HOMA-beta compared to those with an HbA(1c) <48 mmol/mol (91 +/- 52 vs. 120 +/- 88, p = 0.003). No significant between-group difference in HOMA-IR was noted. Conclusions: The use of HbA(1c) in addition to the OGTT in screening for abnormal glucose regulation helped to reveal patients with early beta-cell function impairment.