Racial differences in performance of HbA 1c for the classification of diabetes and prediabetes among US adults of non-Hispanic black and white race

Diabet Med. 2019 Oct;36(10):1234-1242. doi: 10.1111/dme.13979. Epub 2019 Jul 15.


Aim: To characterize differences between black and white people in optimal HbA1c thresholds for diagnoses of diabetes and prediabetes.

Methods: Data were included from the National Health and Nutrition Examination Survey, 2005-2014. Black and white adults (age 18-70 years) who underwent an oral glucose tolerance test and had available fasting plasma glucose, 2-h plasma glucose and HbA1c measurements were eligible for inclusion. Diabetes or prediabetes status was defined by fasting plasma glucose and 2-h plasma glucose using American Diabetes Association criteria. Classification of diabetes, prediabetes and dysglycaemia by HbA1c was evaluated for a range of HbA1c thresholds, with optimal thresholds defined as those values that maximized the sum of sensitivity and specificity (Youden's index).

Results: In 5324 black (32.3%) and white (67.7%) individuals, Youden's index (optimal) thresholds for HbA1c were ≥42 mmol/mol (6.0%) and ≥39 mmol/mol (5.7%) for discriminating diabetes vs non-diabetes, ≥ 44 mmol/mol (6.2%) and ≥39 mmol/mol (5.7%) for discriminating diabetes vs prediabetes (excluding normoglycaemia), ≥39 mmol/mol (5.7%) and ≥37 mmol/mol (5.5%) for discriminating dysglycaemia vs normoglycaemia, and ≥39 mmol/mol (5.7%) and ≥37 mmol/mol (5.5%) for discriminating prediabetes vs normoglycaemia (excluding diabetes), in black and white people, respectively.

Conclusions: Consistently higher optimal HbA1c thresholds in black people than in white people suggest a need to individualize HbA1c relative to glucose levels if HbA1c is used to diagnose diabetes and prediabetes.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Blacks
  • Blood Glucose / analysis
  • Diabetes Mellitus / blood*
  • Diabetes Mellitus / ethnology*
  • Fasting
  • Female
  • Glucose Intolerance / blood
  • Glucose Intolerance / ethnology
  • Glucose Tolerance Test
  • Glycated Hemoglobin A / analysis*
  • Humans
  • Male
  • Nutrition Surveys
  • Prediabetic State / blood*
  • Prediabetic State / ethnology*
  • Racial Groups*
  • Reference Values
  • Sensitivity and Specificity
  • Whites


  • Blood Glucose
  • Glycated Hemoglobin A