A1C is easier to perform than an OGTT, but A1C has a lower rate of detection of diabetes (DM) and prediabetes (preDM). Underperformance of A1C in the detection of hyperglycemia may be magnified in Africans. Three single gene mutations common in Africa, specifically sickle cell trait (SCT), hemoglobin C (HbC) trait and glucose-6-phosphate dehydrogenase (G6PD) deficiency may lead to artefactually low A1C levels. Our goals were: (1) compare DM and preDM prevalence diagnosed by either A1C or OGTT; (2) evaluate whether SCT, HbC trait or G6PD deficiency impact A1C levels. Participants were 421 African-born blacks living in America (male: 66% (276/421), age: 38±10y (mean±SD)). A1C and OGTT were done with repeat studies done in 105 participants 11±7 days later. Diagnosis of DM and preDM required meeting either A1C criteria or glucose guidelines for the OGTT. G6PD activity was assayed in 50 consecutively enrolled participants. DM prevalence was 8% (32/421). Detection of DM by A1C-alone, A1C and OGTT and OGTT-alone were: 16% (5/32), 16% (5/32), and 68% (22/32), respectively. PreDM prevalence was 42% (177/421) with detection rates by A1C-alone, A1C and OGTT and OGTT-alone: 28% (49/177), 30% (53/177) and 42% (75/177), respectively. Repeat testing gave similar results. Among people with DM, 40% (13/32) had either SCT or HbC trait. A1C failed in 77% (10/13) of people with both DM and either SCT or HbC trait. Overall, A1C was 3 times more likely to fail in the detection of DM if either SCT or HbC trait was present (Odds Ratio 3.5 (95% CI: 1.7, 7.5), P<0.01). Prevalence of G6PD deficiency was 16% (8/50). At similar levels of glycemia, A1C levels were lower with G6PD deficiency (4.3±0.1 vs. 5.5±1.0%, P<0.01). Working with African-born blacks living in America, we found that if only A1C was performed, 68% with DM and 42% with preDM would be undiagnosed. SCT, HbC trait and G6PD deficiency contribute to inappropriately low A1C levels and missed opportunity to detect hyperglycemia.
S.M. Briker: None. M.F. Horlyck-Romanovsky: None. J.Y. Aduwo: None. R. Mugeni: None. C. DuBose: None. L. Mabundo: None. S.T. Chung: None. J. Ha: None. A. Sherman: None. A.E. Sumner: None.