Does prediabetes diagnosed by hemoglobinA1c or oral glucose tolerance test predict coronary artery disease in patients suspected of chronic coronary syndrome?

Abstract Introduction The presence of prediabetes worsens the prognosis of coronary artery disease, as patients with prediabetes are known to have an almost doubled cardiovascular mortality risk compared to normoglycemic patients. In clinical practice, HemoglobinA1c (HbA1c) has replaced the oral glucose tolerance test (OGTT) in the diagnosis of prediabetes. However, the background for the HbA1c threshold is based on the development of microvascular complications and progression to established diabetes. It remains unclear whether the substitution of OGTT with HbA1c results in an underestimation of prediabetics with a high risk of coronary artery disease, or if HbA1c is associated with macrovascular complications in prediabetic patients. Purpose We aimed to investigate whether HbA1c- or OGTT-diagnosed prediabetes could predict presence and severity of coronary artery disease in patients suspected of chronic coronary syndrome. Methods This was a descriptive cross-sectional study of 702 patients referred to a coronary CT angiography due to suspicion of chronic coronary syndrome. Coronary artery calcification (CAC)-score, presence of plaque and significant stenosis (>50%), and plaque characteristics were evaluated. All patients had a fasting OGTT and blood samples performed. Patients were categorized according to glycemic status by HbA1c and OGTT, and compared to their test-specific range. Results Prediabetes was detected by HbA1c 167 (24%) or OGTT 272 (39%), and an overlap in classification by both tests was seen in 98 (22%) of participants. Both classifications of prediabetes showed increased presence of plaques, significant stenosis, calcified plaques, and correspondingly, a low frequency of a CAC-score=0 compared to their test-specific normal. Additionally, the HbA1c-prediabetics had an increased frequency of a high CAC score >400 compared to normal HbA1c (23% vs. 10%, p<0.0001). In the multiple logistic regression analysis the HbA1c-prediabetics had an odds ratio (OR) of 1.5 for plaque presence (confidence interval (CI) 1.0;2.4) and OR 2.1 for a CAC-score >400 (CI 1.3;3.5). None of the associations for the OGTT-prediabetics were significant in the logistic regression analysis. Receiver operating characteristic curves were applied to the significant logistic associations. The HbA1c-prediabetics had an area under the curve (AUC)=0.77 for plaque presence and AUC=0.81 for CAC-score >400. Conclusion Prediabetes defined by HbA1c can predict presence and severity of coronary artery disease. Although OGTT identified more patients as having prediabetes, their risk of coronary artery disease was not attributable to prediabetes. Thus, our results support the replacement of OGTT with HbA1c in clinical practice.