Comparison of HbA1c and FPG as a screening tool for diagnosis of pre-diabetes and diabetes in Indian population

Abstract

The aim of this study is to compare hemoglobin A1c (HbA1c) and fasting plasma glucose (FPG) tests as a mass screening tool for pre-diabetes and diabetes as defined by standard oral glucose tolerance test (OGTT). The study was community-based cross-sectional and carried out in urban field practice area of the Department of Community Medicine at Rohtak. A day before the study, subjects were advised to observe overnight fasting (at least 8 h) and were called at the nearest health center in the morning. Initial evaluation included detailed history and clinical examination to exclude any systemic diseases. FPG and 2-h plasma glucose after 75 g OGTT was used to diagnose pre-diabetes and diabetes in 1008 participant. Fasting plasma glucose and 2-h post glucose load were estimated by glucose oxidase method. HbA1c was measured using Cone lab 30i autoanlyser based on latex agglutination inhibition assay (EIA). The American Diabetic Association (ADA) criteria were used to categorize the subjects into pre-diabetes and diabetes (American Diabetes Association. Diabetes Care; 33 Suppl 1:S62–9, 2010). Performance of HbA1c and FPG was evaluated against the results of OGTT by receiver operating characteristics (ROC) curve analysis. The prevalence of pre-diabetes and newly diagnosed diabetes was found 20.6 and 12.5 %, respectively. For pre-diabetes, the area under the ROC curve was 0.831 for HbA1c and 0.807 for FPG (p value 0.205), whereas for diabetes, these values were 0.957 for HbA1c and 0.942 for FPG (p value 0.11). At the optimal HbA1c cutoff points of 5.4 % for pre-diabetes and of 6.2 % for newly diagnosed diabetes, sensitivities and specificities were 79.02, 79.31 and 94.24, 90.52 %, respectively. Similarly, FPG optimal cutoff points of ≥97 mg/dl for pre-diabetes and ≥119 mg/dl for diabetes were found to have maximum sensitivities (specificities) of 93.13 (63.32) and 93.53 (89.64), respectively. It is observed that at optimal cutoff of FPG ≥97 mg/dl and HbA1c ≥5.4 % for pre-diabetes and ≥119 mg/dl and 6.2 % for newly diagnosed diabetes, more true-positive cases are identified as compared to currently recommended ADA criteria when both were compared with results of 75 g OGTT. As a screening tool for newly diagnosed pre-diabetes and diabetes, the HbA1c measurement did not perform inferior than FPG. In this study population, FPG and HbA1c values lower than the currently recommended values of ADA were found to be better predictor of pre-diabetes and diabetes.