Abstract P115: Prevalence of Undiagnosed Diabetes Decreases by Eighty Percent When A1C Replaces the OGTT: The Africans in America Study

Introduction: Africa has the highest prevalence of undiagnosed diabetes (DM) in the world. It is unknown whether programs designed to screen for DM in Africa should rely on hemoglobin A 1C (A1C) or the 2h oral glucose tolerance test (OGTT). In general, the prevalence of undiagnosed DM is lower when detection is based on A1C rather than the OGTT. However, the degree to which the prevalence of undiagnosed DM would be lower in Africans if A1C rather than the OGTT was used is unknown. Heterozygous hemoglobinopathies such as sickle cell trait (SCT) and hemoglobin C (HbC) trait may lower A1C independent of the degree of glycemia, potentially compromising the ability of A1C to detect DM. Objective: Our goals were to determine in Africans the rate of detection and reproducibility of the diagnosis of DM by both A1C and OGTT. Methods: Ninety African-born blacks (66% (59/90) male, age 40±11y (mean±SD), BMI 27.6±4.6 kg/m 2 ) who self-identified as healthy, currently live in the Washington DC area and enrolled in the Africans in America study had two OGTT performed 10±8 days apart. At both visits A1C was assayed by HPLC from whole blood and glucose from plasma samples taken at -15, 0, 30, 60, 90 and 120 minutes. For A1C, DM was diagnosed by levels ≥6.5%. For the OGTT, fasting glucose ≥126 mg/dL or 2h glucose≥200 mg/dL was required to diagnose DM. The κ-statistic was used to evaluate reproducibility. Hemoglobin electrophoresis was performed. Results: At Visit 1: DM was diagnosed by A1C in 4% (4/90) and by OGTT in 26% (23/90). At Visit 2: DM was diagnosed by A1C in 3% (3/89) and by OGTT in 21% (19/90). Diagnosis by A1C and OGTT displayed substantial (κ=0.74) and almost perfect (κ=0.88) reproducibility, respectively. All persons with DM diagnosed by A1C criteria at either visit were also diagnosed by OGTT. However, 83% (19/23) of people with DM diagnosed by OGTT were not detected by A1C. In the entire cohort the combined prevalence of HbS and HbC trait was 14% (13/90). However, the prevalence of SCT and HbC trait in people with DM diagnosed by OGTT was 42% (8/19), but no one with SCT or HbC trait had an A1C level≥6.5%. Conclusion: Diagnosis of DM by both A1C and OGTT are highly reproducible in African immigrants. However, A1C detects 80% fewer people with DM than does the glucose criteria for the OGTT. The clinical consequences of this lower rate of detection of DM by A1C remains to be determined in prospective studies.