HbA1c Test Misses Many Cases of Diabetes

A glucose tolerance test, also known as the oral glucose tolerance test, measures the body's response to sugar (glucose). In this test, a person's blood is taken after an overnight fast, and then again two hours after they drink a sugary drink. The glucose tolerance test can be used to screen for type 2 diabetes.

The glycated hemoglobin (HbA1c) test shows the average level of blood sugar over the past two to three months. People who have diabetes usually have this test to see whether their blood sugar levels have been staying within a target range. This test is also used to diagnose type 1 and type 2 diabetes. It is often used to diagnose diabetes because no fasting or any preparation is required.


Endocrinologists at the City of Hope's Diabetes and Metabolism Research Institute (Duarte, CA, USA) included 9,000 adults without a diabetes diagnosis in a new study. The participants got both an HbA1c test and an oral tolerance glucose test, and the team compared the results. They found the HbA1c test did not catch 73% of diabetes cases that were detected by the oral glucose test. They found race and ethnicity had a significant impact on the accuracy of HbA1c. It was more likely to detect abnormal glucose levels in non-Hispanic whites than in non-Hispanic blacks or Hispanics.

Maria Mercedes Chang Villacreses, MD, the lead author of the study, said, “Based on our findings, HbA1c should not be solely used to determine the prevalence of diabetes. It should be used in conjunction with the oral glucose test for increased accuracy. The HbA1c test said some people had normal glucose levels when they didn't. Our results indicated that the prevalence of diabetes and normal glucose tolerance defined solely by HbA1c is highly unreliable, with a significant tendency for underestimation of the prevalence of diabetes and overestimation of normal glucose tolerance.” The study was presented on March 23, 2019, at the Endocrine Society's annual meeting held in New Orleans, LA, USA.

Related Links:
City of Hope's Diabetes and Metabolism Research Institute