1600-P: Duplicate Oral Glucose Tolerance Tests Reveal Excellent Reproducibility for Detection of Diabetes but Inconsistent Results for Prediabetes: A Study of Africans

As both diabetes (DM) and prediabetes (preDM) reach epidemic proportions in sub-Saharan Africa, there is growing need for reliable diagnostic tests. Although the OGTT is time-consuming, it is unaffected by hemoglobinopathies which are common in Africa and interfere with other methods of detection. However, the reproducibility of the OGTT in Africans is unknown. Therefore, our goal was to perform duplicate OGTTs in Africans and determine if the diagnosis made at the first OGTT was confirmed by the second. One-hundred and five African-born blacks (64% male (67/105), age 39±11y (mean±SD), BMI 27.4±4.5 kg/m²) living in the Washington, DC area had two OGTTs performed 11±7 days apart. Glucose tolerance status was defined by glucose criteria for the OGTT. κ-statistic was used to assess reproducibility (slight: 0.00 to 0.20; fair: 0.21 to 0.40; moderate: 0.41 to 0.60; substantial: 0.61 to 0.80, excellent: 0.81 to 1.0). At OGTT-1, DM, preDM and normal glucose tolerance (NGT) occurred in 23% (24/105), 26% (27/105) and 51% (54/105), resp. At OGTT-2, DM, preDM and NGT occurred in 19% (20/105), 26% (27/105) and 55% (58/105) resp. Reproducibility for the diagnosis of DM was excellent (κ=0.88). No one transitioned from DM to NGT. Further, all participants with DM at OGTT-2 had also been diagnosed with DM at OGTT-1. In contrast, reproducibility for the diagnosis of preDM was only moderate (κ=0.48). Between OGTT-1 and OGTT-2, 10% (11/105) of people transitioned from preDM to NGT; and 7% (7/105) transitioned from NGT to preDM. However, 78% (14/18) of the people who transitioned between NGT and preDM had fasting glucose levels between 90 and 99 mg/dL. Overall, as duplicate OGTTs provided highly reproducible results for the diagnosis of DM, detection of DM by a single OGTT should trigger health care consideration. Diagnosis of preDM was not consistent, but fasting glucose between 90 mg/dL and 99 mg/dL suggests that transition from NGT to preDM is likely.