Oral glucose tolerance test and HbA1c for diagnosis of diabetes in patients undergoing coronary angiography the Silent Diabetes Study

The primary aim of this study was to compare the results of HbA(1c) measurements with those of an OGTT for early diagnosis of 'silent diabetes' in patients with coronary artery disease (CAD) undergoing angiography without prediagnosed diabetes. A secondary aim was to investigate the correlation between the extent of CAD and the glycaemic status of the patient. Data from 1,015 patients admitted for acute (n = 149) or elective (n = 866) coronary angiography were analysed. Patients with known diabetes were excluded from the study. Using the OGTT results, patients were classified as having normal glucose tolerance (NGT), impaired fasting glucose (IFG), impaired glucose tolerance (IGT) or diabetes. According to the results of the HbA(1c) measurements, patients were classified into three groups: normal (HbA(1c) < 5.7% [< 39 mmol/mol]), borderline (HbA(1c) 5.7-6.4% [39-47 mmol/mol]) and diabetes (HbA(1c) a parts per thousand yen6.5% [a parts per thousand yen48 mmol/mol]). Based on the OGTT, 513 patients (51%) were classified with NGT, 10 (1%) with IFG, 349 (34%) with IGT and 149 (14%) were diagnosed with diabetes. According to HbA(1c) measurements, 588 patients (58%) were classified as normal, 385 (38%) as borderline and 42 (4%) were diagnosed with diabetes. The proportion of patients with IGT and diabetes increased with the extent of CAD (IGT rho = 0.14, p < 0.001, diabetes rho = 0.09, p = 0.01). No differences in HbA(1c) were seen among the groups with different extents of CAD (p = 0.652). An OGTT should be performed routinely for diagnosis of diabetes in patients with CAD undergoing coronary angiography, since HbA(1c) measurement alone appears to miss a substantial proportion of patients with silent diabetes. A limitation of the study is that the OGTT was not performed before the angiography.