Hemoglobin A1c blood test does not detect diabetes in most patients, shows study

The hemoglobin A1c blood test is widely used to diagnose type 1 and type 2 diabetes, but it is actually unable to detect the disease in most patients, according to a new study presented Saturday, March 23, at a news conference at ENDO 2019, the Endocrine Society's annual meeting in New Orleans, La.

"Based on these findings, A1c should not be solely used to rule out diabetes, particularly if a patient has prediabetes or has increased risk factors for developing diabetes," said lead researcher Maria Mercedes Chang Villacreses, M.D., of City of Hope's Diabetes and Metabolism Research Institute, who presented at the press conference. "It should be used in conjunction with the oral glucose test for increased accuracy."

Led by Ken C. Chiu, M.D., City of Hope professor of clinical diabetes, endocrinology & metabolism, the study included 9,000 adults from the 2005-2014 National Health and Nutrition Examination Survey who did not have a diabetes diagnosis. The participants received both an A1c test and an oral tolerance glucose test, and the researchers compared the results. The researchers found the A1c test didn't catch 73 percent of diabetes cases that were detected by the oral glucose test.

"The A1c test showed these people had normal glucose levels when they didn't," Chang Villacreses said.

The hemoglobin A1c test, also known as HbA1c, shows a person's average level of blood sugar over the past two to three months. The test is used to diagnose diabetes, and also to find out whether a person with the disease has blood sugar levels within a certain target range. The simple blood test has grown in popularity because it doesn't require patients to fast, unlike the two other most common diabetes tests.

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 researchers also found race and ethnicity had a significant impact on the accuracy of A1c. It was more likely to detect abnormal glucose levels in non-Hispanic whites than in non-Hispanic blacks or Hispanics.

"We want to diagnose diabetes earlier so we can intervene earlier and potentially prevent diabetic complications from developing," Chang Villacreses said. "The best way to do that is by also using oral glucose tests."

According to the Centers for Disease Control and Prevention, 30.3 million U.S. adults have diabetes, and one in four of them don't know they have it. Diabetes is the seventh leading cause of death in the United States, and is the leading cause of kidney failure, lower-limb amputations and adult blindness. In the last 20 years, the number of adults diagnosed with diabetes has more than tripled.

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