Use of Glycated Hemoglobin in the Diagnosis of Diabetes Mellitus and Pre-diabetes and Role of Fasting Plasma Glucose, Oral Glucose Tolerance Test

The study goal was to clarify the power and efficacy of glycated hemoglobin (HbA1c) in the diagnosis of diabetes and pre-diabetes by comparing against the other American Diabetes Association (ADA) diagnostic criteria of fasting plasma glucose (FPG) and oral glucose tolerance test (OGTT). This is a retrospective study. A total of 27,001 individuals attended to the internal medicine outpatient clinic between 2006 and 2010 years were screened. All diabetic patients and those using drugs associated with the development of diabetes were excluded. The results of FPG, OGTT and A1c for 1814 individual were analyzed and all grouped as diabetic patients, glucose intolerant (pre-diabetes) patients and non-diabetic patients according to new ADA criteria for the diagnosis of diabetes. The prevalence of newly diagnosed diabetes was 69.6% and 54% by using HbA1c alone, 64.2% and 28.2% with 2-h OGTT alone and 43.2% and 60.3%, respectively with FPG alone. Differences between FPG versus 2-h OGTT, FPG versus A1c and OGTT versus A1c were statistically significant (P < 0.0001, P < 0.0001 and P = 0.02, respectively). Diagnostic sensitivity of all diabetic criteria was 69.6% for A1c; Nearly, 64.2% for OGTT and only 43.1% for FPG respectively. In terms of diagnostic ratio of glucose intolerance; difference between HbA1C and OGTT was statistically significant (P < 0.0001). As a screening tool for newly diagnosed diabetes and pre-diabetes, the HbA1C level performed better than FPG and 2-h OGTT in this general Saudi population. High diagnostic power of A1C may contribute to the decrease in the number of undiagnosed patients.