title: Detection of abnormal glucose tolerance in Africans is improved by combining A1C with fasting glucose: the Africans in America Study.
abstract: OBJECTIVE
  Abnormal glucose tolerance is rising in sub-Saharan Africa. Hemoglobin A1c by itself and in combination with fasting plasma glucose (FPG) is used to diagnose abnormal glucose tolerance. The diagnostic ability of A1C in Africans with heterozygous variant hemoglobin, such as sickle cell trait or hemoglobin C trait, has not been rigorously evaluated. In U.S.-based Africans, we determined by hemoglobin status the sensitivities of 1) FPG ≥5.6 mmol/L, 2) A1C ≥ 5.7% (39 mmol/mol), and 3) FPG combined with A1C (FPG ≥5.6 mmol/L and/or A1C ≥5.7% [39 mmol/mol]) for the detection of abnormal glucose tolerance.
  
  
  METHODS
  An oral glucose tolerance test (OGTT) was performed in 216 African immigrants (68% male, age 37 ± 10 years [mean ± SD], range 20-64 years). Abnormal glucose tolerance was defined as 2-h glucose ≥7.8 mmol/L.
  
  
  RESULTS
  Variant hemoglobin was identified in 21% (46 of 216). Abnormal glucose tolerance occurred in 33% (72 of 216). When determining abnormal glucose tolerance from the OGTT (2-h glucose ≥7.8 mmol/L), sensitivities of FPG for the total, normal, and variant hemoglobin groups were 32%, 32%, and 33%, respectively. Sensitivities for A1C were 53%, 54%, and 47%. For FPG and A1C combined, sensitivities were 64%, 63%, and 67%. Sensitivities for FPG and A1C and the combination did not vary by hemoglobin status (all P > 0.6). For the entire cohort, sensitivity was higher for A1C than FPG and for both tests combined than for either test alone (all P values ≤ 0.01).
  
  
  CONCLUSIONS
  No significant difference in sensitivity of A1C by variant hemoglobin status was detected. For the diagnosis of abnormal glucose tolerance in Africans, the sensitivity of A1C combined with FPG is significantly superior to either test alone.
authors.affiliation: Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD annes@intra.niddk.nih.gov.
authors.forename: Anne E
authors.initials: AE
authors.lastname: Sumner
authors.affiliation: Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD.
authors.forename: Caroline K
authors.initials: CK
authors.lastname: Thoreson
authors.affiliation: Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD.
authors.forename: Michelle Y
authors.initials: MY
authors.lastname: O'Connor
authors.affiliation: Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD.
authors.forename: Madia
authors.initials: M
authors.lastname: Ricks
authors.affiliation: Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD.
authors.forename: Stephanie T
authors.initials: ST
authors.lastname: Chung
authors.affiliation: Tropical Medicine Research Institute, University of the West Indies, Kingston, Jamaica.
authors.forename: Marshall K
authors.initials: MK
authors.lastname: Tulloch-Reid
authors.affiliation: Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, MD.
authors.forename: Jay N
authors.initials: JN
authors.lastname: Lozier
authors.affiliation: Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, MD.
authors.forename: David B
authors.initials: DB
authors.lastname: Sacks
mesh_terms: D000328:Adult; D000349:Africa / Q000208:ethnology; D001786:Blood Glucose / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D005215:Fasting / Q000097:blood; D005260:Female; D005947:Glucose; D018149:Glucose Intolerance / Q000097:blood / Q000175:diagnosis* / Q000208:ethnology; D005951:Glucose Tolerance Test; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D014481:United States; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D005947:Glucose; D006442:Glycated Hemoglobin