City of Hope Researchers: Popular Diabetes Diagnosis Test Misses 73% of Cases

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By : Suvarna Sheth

The hemoglobin A1c blood test, widely used to diagnose Type 1 and Type 2 diabetes, is actually unable to detect the disease in most patients, according to a new study by City of Hope researchers.

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.

How was the Study Conducted?

Researchers conducted a study which 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. They found the A1c test did not 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,” lead researcher, Dr. Maria Mercedes Chang Villacreses tells dLife. “A very significant number of people missed diagnosis, and we want to increase awareness about this so physicians do not solely rely on the A1C test and evaluate results on individualized manner for best patient care, instead.”

Based on these findings, Chang Villacreses says A1c should not be solely used to rule out diabetes, particularly if a patient has prediabetes or has increased risk factors for developing diabetes.

Instead, the researcher at City of Hope’s Diabetes and Metabolism Research Institute says the test should be used in conjunction with the oral glucose test for increased accuracy.

“Because of its convenience, the A1C test has become the primary method of screening and diagnosis for diabetes,” Chang Villacreses says. “The ADA does have statements about not relying solely on the A1C test but we wanted to bring more awareness to this.”

She indicates the current guidelines recommend screening for diabetes on people >45 years old or who have risk factors, using either test, but due convenience and reliability A1C has been more widely used nowadays.

She says most endocrinology practices are aware of the sensitivity of the test, but because primary care physicians are also managing a lot of diabetes, it is important to bring this up as an “alert” for them too.

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.

When asked why race has a significant impact on the accuracy of A1C, Chang Villacreses told dLife they do not have an explanation for this difference, but it is worth further investigation.

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

She adds the current diagnostic methods also have room for more investigation.

The research was presented Saturday, March 23, at a news conference at ENDO 2019, the Endocrine Society’s annual meeting in New Orleans, La.


  1. City of Hope Study Finds Popular Diabetes Diagnosis Test Misses Most Cases. (March 23, 2019). BusinessWire. Retrieved: