The Compatibility of Hemoglobin A1c with Oral Glucose Tolerance Test and Fasting Plasma Glucose

Objectives: Diabetes mellitus (DM) is a chronic metabolic disease requiring lifelong medical care, and its prevalence is increasing worldwide. Early diagnosis of prediabetes and diabetes is significant in view of the mortality, morbidity and cost associated with them. Because of the difficulties in application and reproducibility of oral glucose tolerance test (OGTT), which is considered to be the gold standard in the diagnosis of DM, more feasible diagnostic tests are needed. This study aims to evaluate the validity of hemoglobin A1c (HbA1c) in predicting prediabetes and diabetes in the Turkish population and to evaluate the compatibility of HbA1c with other diagnostic tests. Methods: The patients who were admitted to Health Sciences University Sisli Hamidiye Etfal Training and Research Hospital internal diseases and endocrinology outpatient clinics between 01.01.2013 and 30.06.2014 enrolled in this study. The participants were >18 years of age and were not diagnosed with prediabetes or DM earlier. The results of OGTT, fasting plasma glucose (FPG) and HbA1c tests were retrospectively screened, and the correlation of them was analyzed. Results: In this study, 201 participants enrolled. Of these cases, 127 were women and 74 were men. Mean age of the group was 49.3 +/- 10.4 years. HbA1c was observed <5.7% in the 15%, 5.7-6.4% in the 60%, and >= 6.5% in the 25% of the cases. While FPG was <100 mg/dL in 24% of the participants, it was found to be between 100-126 mg/dL in 71% and >= 126 mg/dL in 5% of the participants. According to the OGTT data, 23% of the cases were healthy, 59% were prediabetic and 18% were diabetic. The sensitivity and specificity of HbA1c were calculated as 50% and 80%, respectively. While the sensitivity of FPG was 17% and specificity was 97%. Conclusion: The data obtained from our study show that HbA1c is a more sensitive test compared to FPG in the diagnosis of DM. Prospective studies with broad participation at national and international levels are needed to redefine HbA1c cut- off points for the diagnosis of DM and prediabetes. Thus, it will be possible to revise the diagnostic guidelines accordingly.