title: Implications of iron deficiency/anemia on the classification of diabetes using HbA1c.
abstract: OBJECTIVE
  Nonglycemic factors like iron deficiency (ID) or anemia may interfere with classification of diabetes and prediabetes using hemoglobin A1c (HbA1c). However, few population-based studies of diabetes in areas with endemic ID/anemia have been conducted. We aimed to determine how mutually exclusive categories of ID alone, anemia alone and iron-deficiency anemia (IDA) were each associated with prediabetes and diabetes prevalence using fasting blood glucose (FBG) versus HbA1c in a population-based study of adults with endemic ID/anemia.
  
  
  METHODS
  We used data from the China Health and Nutrition Survey, a longitudinal, population-based study across 228 communities within nine provinces of China. This analysis included 7308 adults seen in the 2009 survey aged 18-75 years. We used descriptive and covariate-adjusted models to examine relative risk of prediabetes and diabetes using FBG alone, HbA1c alone, HbA1c and FBG, or neither (normoglycemia) by anemia alone, ID alone, IDA or normal iron/hemoglobin.
  
  
  RESULTS
  Approximately 65% of individuals with diabetes in our sample were concordantly classified with diabetes using both FBG and HbA1c, while 35% had a discordant diabetes classification: they were classified using either FBG or HbA1c, but not both. Fewer participants with ID alone versus normal iron/hemoglobin were classified with diabetes using HbA1c only. From covariate-adjusted, multinomial regression analyses, the adjusted prevalence of prediabetes using HbA1c only was 22% for men with anemia alone, but 13% for men with normal iron/hemoglobin. In contrast, the predicted prevalence of prediabetes using HbA1c only was 8% for women with ID alone, compared with 13% for women with normal iron/hemoglobin.
  
  
  CONCLUSIONS
  These findings suggest potential misclassification of diabetes using HbA1c in areas of endemic ID/anemia. Estimating diabetes prevalence using HbA1c may result in under-diagnosis in women with ID and over-diagnosis in men with anemia.
authors.affiliation: Department of Nutrition, Gillings School of Global Public Health, UNC-Chapel Hill, Chapel Hill, NC, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Attard
authors.affiliation: 1] Carolina Population Center, UNC-Chapel Hill, Chapel Hill, NC, USA [2] Department of Biostatistics, Gillings School of Global Public Health, UNC-Chapel Hill, Chapel Hill, NC, USA.
authors.forename: A H
authors.initials: AH
authors.lastname: Herring
authors.affiliation: National Institute of Nutrition and Food Safety, Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.affiliation: 1] Carolina Population Center, UNC-Chapel Hill, Chapel Hill, NC, USA [2] Department of Biostatistics, Gillings School of Global Public Health, UNC-Chapel Hill, Chapel Hill, NC, USA.
authors.forename: A-G
authors.initials: AG
authors.lastname: Howard
authors.affiliation: 1] Carolina Population Center, UNC-Chapel Hill, Chapel Hill, NC, USA [2] Department of Anthropology, UNC-Chapel Hill, Chapel Hill, NC, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Thompson
authors.affiliation: 1] Department of Nutrition, Gillings School of Global Public Health, UNC-Chapel Hill, Chapel Hill, NC, USA [2] Carolina Population Center, UNC-Chapel Hill, Chapel Hill, NC, USA.
authors.forename: L S
authors.initials: LS
authors.lastname: Adair
authors.affiliation: 1] Department of Nutrition, Gillings School of Global Public Health, UNC-Chapel Hill, Chapel Hill, NC, USA [2] Department of Medicine, UNC-Chapel Hill, Chapel Hill, NC, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Mayer-Davis
authors.affiliation: 1] Department of Nutrition, Gillings School of Global Public Health, UNC-Chapel Hill, Chapel Hill, NC, USA [2] Carolina Population Center, UNC-Chapel Hill, Chapel Hill, NC, USA.
authors.forename: P
authors.identifier: 0000000153224188
authors.initials: P
authors.lastname: Gordon-Larsen