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Study: As a diagnostic test, A1C often misses diabetes

A photo of diabetes-related supplies, including packets of pills, a bottle of pills, needles, test strips and a meter for testing blood sugar levels.

April 15, 2019—The A1C blood test is one of the tools used to diagnose diabetes. But according to the results of a new study, the test fails to catch many cases of the disease.

The A1C test measures a person's average blood sugar level over the past two to three months. In people who already know they have diabetes, the A1C test is used to help them stay on top of their blood sugar goals.

But in addition to its use as a diabetes management tool, the A1C test is sometimes used to diagnose diabetes. Unlike some other diabetes screening tests, there's no need to fast overnight for the A1C test. So it's quick and simple to use.

Head-to-head tests

For the study, researchers compared 9,000 adults without a diabetes diagnosis. The participants took both the A1C test and an oral glucose tolerance test (OGTT). For the OGTT, a patient's blood is drawn after an overnight fast and again, after they consume a sugary drink, two hours later.

Among the key findings of the study:

  • The A1C test missed 73 percent of diabetes cases that the oral glucose test detected.
  • The A1C test was more accurate in non-Hispanic whites than in Hispanics or non-Hispanic blacks.

When it comes to diagnosing diabetes, the A1C blood test should only be used along with the oral glucose test, the researchers contend.

Their study was presented at the annual meeting of the Endocrine Society.

Talk to your doctor

It's important to get checked for diabetes if you have symptoms or risk factors. Your doctor can answer any questions you may have about diabetes testing options.

Currently, using the A1C test by itself is one option to diagnose type 2 diabetes and a related condition called prediabetes. Or it can be used in combination with other diabetes tests, such as the OGTT and the fasting plasma glucose test.

Because different tests may give different results, doctors often must repeat a diabetes test to confirm a diagnosis.

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