Comparison between the Oral Glucose Tolerance Test and the Hba1c Assay for Detecting Impaired Glucose Regulation in Bahamian Adolescents

Abstract

Objective: To determine the best method for detecting Impaired Glucose Regulation (IGR) in adolescents from New Providence Island, Bahamas. IGR is defined by blood glucose levels that are higher than normal but below those of a person with diabetes. Design and Methods: From Jan-March 2012, 873 adolescents (13-19 years old) were randomly selected from five different high schools in New Providence. Weight and height were measured and participants were screened for IGR using the hemoglobin A1c (HbA1c) test and a 2-hour oral glucose tolerance test (OGTT). T-test or chi-square test was used to determine significant associations between sex and outcome variables, and prevalence of glycemic status by BMI category. Linear regression was used to determine the relationship between OGTT results and BMI. Results: Of the initial pool, 861 adolescents (98.6%) completed the study. The OGTT demonstrated that 89.4% of these students had normal fasting glucose levels and 98.8% had normal 2-hour OGTT glucose levels. Eightyseven students (37 boys and 50 girls) had elevated fasting plasma glucose; however, 2 hours after the oral glucose load, only 9 students (2 boys and 7 girls) had blood glucose concentrations indicative of IGR. For the HbA1c test, 82.6% of the students had normal results, and 1.3% had diabetes. The HbA1c test revealed a higher percentage of students with IGR (16.1%) than the OGTT (1%). Conclusions: The HbA1c test identified a greater percentage of adolescents as having IGR than did the OGTT. Due to the high discordance between the two tests, it is likely that an elevated HbA1c test may falsely classify adolescents as IGR if OGTT results and clinical signs (e.g., diabetic retinopathy and/or nephropathy) are not considered.