HbA1c Test Significantly Underestimates Diabetes Prevalence

Investigators examined glucose tolerance defined by hemoglobin A1c to the oral glucose tolerance test.

The prevalence of diabetes and normal glucose tolerance defined solely by hemoglobin A1c (HbA1c) is highly unreliable, according to an abstract presented at ENDO 2019: The Endocrine Society Annual Meeting, held March 23 to 26 in New Orleans, Louisiana.1

Using a sample of 9000 adults without a diabetes diagnosis from the National Health and Nutrition Examination Survey taken between 2005 and 2014, researchers compared states of glucose tolerance defined by the HbA1c test and the oral glucose tolerance test (OGTT). Criteria for normal glucose tolerance, prediabetes, and diabetes were defined using the American Diabetes Association guidelines.

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The distribution of glucose tolerance states defined by HbA1c and OGTT differed significantly (P <.000001). Compared with the OGTT, the sensitivity for the diagnosis of diabetes by HbA1c was 26.93% with a specificity of 99.39%. The HbA1c test misclassified 73.07% of diabetes cases that were detected by the OGTT, thus significantly underestimating the true prevalence of diabetes defined by OGTT.

Compared with the OGTT, the sensitivity for the diagnosis of normal glucose tolerance by HbA1c was 84.91% with a specificity of 43.53%. Of the 6300 individuals identified as having normal glucose tolerance by HbA1c, only 57.52% were detected by the OGTT. Therefore, the HbA1c criteria significantly overestimated the true prevalence of normal glucose tolerance compared with the OGTT.

Furthermore, race and ethnicity had a significant effect on the sensitivity of HbA1c criteria, as it was more likely to detect abnormal glucose levels in non-Hispanic whites than in non-Hispanic blacks or Hispanics.

“Based on our findings, A1c should not be solely used to determine the prevalence of diabetes,” said lead researcher Maria Mercedes Chang Villacreses, MD, from City of Hope in Duarte, California, in a press release.2 “It should be used in conjunction with the oral glucose test for increased accuracy.”

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1. Chang Villacreses MM, Feng W, Karnchanasorn R, Samoa R, Chiu KC. Underestimation of the prevalence of diabetes and overestimation of the prevalence of glucose tolerance by using hemoglobin A1c criteria. Presented at: ENDO 2019; March 23-26, 2019; New Orleans, LA. Abstract SAT-125.

2. A1c test misses many cases of diabetes [press release]. Washington, DC: Endocrine Society; March 23, 2019. Accessed March 23, 2019.