Performance of Hba1c Versus Oral Glucose Tolerance Test (Ogtt) as a Screening Tool to Diagnose Dysglycemic Status

Abstract

Background: Increasing global prevalence of type 2 diabetes (T2D) has resulted in concerted efforts to improve predictors for development of this obesity-related disorder. Establishing markers that identify prediabetes, an intermediary state of glycaemia above that of healthy individuals but below frank T2D, is an important focus. The objectives of this study were to examine the diagnostic accuracy of HbA1c using OGTT as a reference standard to identify subjects of dysglycemic status and also evaluate the agreement between HbA1c and OGTT in diagnosing dysglycemic status among high-risk Indian patients.
 Methods: We reviewed a sample of high-risk adult, aged 18 Yrs and older, who underwent 75-g OGTT and had an HbA1c value. Data were collected on baseline characteristics such as, age, sex, blood pressure, BMI, WC, history of diabetes in first-degree relatives, previously documented cardiovascular diseases, history of smoking, hypertension, plasma lipid profiles, and statin usage.
 Results: We evaluated the agreement represented by the ROC curves between the classification of prediabetes and diabetes defined by OGTT and HbA1c. In diabetes group, the AUC was 0.73 indicating that HbA1c was an acceptable test to diagnose diabetes. The agreement, represented by kappa value of 0.312 , was considered a fair agreement between the two tests. However in diagnosing prediabetes, AUC from the ROC curve is 0.52. Thus, HbA1c could not be used to discriminate subjects with IGT. The Kappa value of 0.153, indicated that there was no agreement between the two tests in diagnosing prediabetes.
 Conclusion: Our study found that diabetes prevalence is higher when diagnosed using OGTT than when using HbA1c which implies the limitations of HbA1c as a screening tool for diabetes in high-risk patients. This is the first study to explore the role of HbA1c in diagnosing dysglycemic status in high-risk patients. OGTT should continue to advocate as a screening tool for identification of dysglycemic status in particular population.
 Keywords: HbA1c, OGTT, Dysglycemia.