Hemoglobin C (HbC) trait is a Hb variant found in 15% of West Africans. Similar to HbS, HbC occurs because of a single nucleotide substitution on the beta-globin chain of hemoglobin. Many studies have evaluated whether HbS trait influences the diagnostic efficacy of A1C. Data on the effect of HbC trait on A1C is scant. Our goal was to determine by Hb-type the sensitivity and specificity of A1C as a diagnostic test for the detection of abnormal glucose tolerance (abnl-GT) in 369 blacks born in Africa and currently living in the Washington, DC area (age 38±10y (mean±SD), BMI 27.5±4.5 kg/m2). OGTT and Hb electrophoreses were performed. Abnl-GT was defined as fasting glucose≥100 mg/dL or 2h glucose≥140 mg/dL. A1C ≥5.7% was considered diagnostic for abnl-GT. The frequencies of normal Hb-type, HbS trait and HbC trait were: 82%, 14% and 4%, respectively. The prevalence of abnl-GT in each group was: 38%, 42%, and 50% (P=0.59), respectively. Sensitivity and specificity of A1C by group are provided in the Table. No one in the HbC trait group with abnl-GT was detected by A1C. Hence, sensitivity was 0%. Furthermore, specificity of A1C in the HbC trait group was 100% as no one with normal glucose tolerance had A1C≥5.7%. The number of individuals with HbC trait was small but our findings suggest the need for greater investigation into the diagnostic efficacy of A1C in the presence of HbC trait.

S.M. Briker: None. J. Kabakambira: None. R.L. Baker: None. C. DuBose: None. L. Mabundo: None. S.T. Chung: None. D.B. Sacks: Other Relationship; Self; Sebia, Trinity Biotech. A.E. Sumner: None.

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