Abstract 13: Detection of Abnormal Glucose Tolerance Status in Africans is improved by combining A1C with Fasting Glucose
Diabetes is reaching epidemic proportions in Africa. Therefore it is critical to invest scarce resources in effective tests. Both the World Health Organization and the American Diabetes Association have approved A1C and fasting plasma glucose (FPG) as diagnostic alternatives to the OGTT for the detection of pre-diabetes and diabetes. However, A1C thresholds for the diagnosis of abnormal glucose tolerance are dependent on >90% of hemoglobin (Hb) being HbA. This could be problematic for Africans, as the prevalence of variant Hb including both sickle (S) and HbC are high. When either HbS or HbC is present as a trait, the concentration of HbA is usually<60%. Our goal was to test in African immigrants whether A1C or A1C combined with FPG have sufficient sensitivity to be an effective diagnostic alternative to the OGTT. Two hundred and six self-identified healthy Africans living in the Washington DC area (140 men, 66 women, age 36±10y (mean±SD, range 20-64y) were enrolled. The African region of origin for the participants was West 57% (112 of 206), Central 27% (56 of 206) and East 19% (38 of 206). Every participant had an OGTT. HPLC was performed to determine the presence of variant Hb and A1C levels. Variant Hb occurred in 21% (44 of 206) of Africans. FPG, 2h glucose and A1C were: 90±13 mg/dL, 131±40 mg/dL and 5.5±0.7% respectively. On the basis of the OGTT, 30% (61 of 206) had newly identified pre-diabetes and 6% (12 of 206) had diabetes. For the detection of abnormal glucose tolerance, the pre-diabetic and diabetic participants were combined into a single group. For comparison to the OGTT, diagnostic thresholds were FPG≥100 mg/dL and A1C≥5.7%. In Africans without variant Hb, the sensitivity for the diagnosis of abnormal glucose tolerance by A1C was 53%. In the presence of variant Hb, the sensitivity of A1C to detect abnormal glucose tolerance fell to 40%. When either A1C or FPG were positive, sensitivity for the diagnosis of abnormal glucose tolerance in Africans with and without variant Hb was 67% and 64%, respectively. In short, A1C alone is not a satisfactory diagnostic test in Africans and this was magnified in the presence of variant Hb. However, when A1C was combined with FPG the sensitivity rose to the mid-sixties and did not vary by variant Hb status. Thus, to detect abnormal glucose tolerance status in Africans combining A1C with FPG makes it unnecessary to know variant Hb status and improves diagnostic capability.
Author Disclosures: A.E. Sumner: None. C.K. Thoreson: None. M.Y. O'Connor: None. M. Ricks: None. S.T. Chung: None. J. Lozier: None. D.B. Sacks: None.
- © 2014 by American Heart Association, Inc.