A1C Blood Test OK for Diabetes Diagnosis

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New Guidelines Call for Using A1C Blood Test to Identify People With Prediabetes

By Salynn Boyles
WebMD Health News

Reviewed By Brunilda Nazario, MD

Dec. 29, 2009 -- The American Diabetes Association (ADA) is recommending that a simple blood test currently used to assess whether diabetes is under control also be used to diagnose the disease.

The blood test -- known as the A1C test -- has several important advantages over traditional blood glucose testing.

Patients do not need to fast before the test is given, and it is far less likely to identify clinically irrelevant fluctuations in blood sugar because it measures average blood glucose levels over several months.

The new guidelines do not call for replacing traditional screening with the A1C test.

It is believed that around 6 million Americans have diabetes but don't know it, and another 57 million have prediabetes.

The A1C test may help identify a large number of people in both of these groups, former ADA president for medicine and science John Buse, MD, PhD, tells WebMD.

Buse, who is chief of endocrinology at the University of North Carolina, Chapel Hill, helped draft the new ADA diabetes care guidelines, which were made public today.

"We now know that early diagnosis and treatment can have a huge impact on outcomes by preventing the complications commonly seen when diabetes is not well controlled," he says. "Our hope is that people with early or prediabetes who might otherwise not be tested would have the A1C test."

How the A1C Test Works

The A1C test has been used since the late 1970s as a measure of how well diabetes is managed, but the ADA had not previously recommended it for diagnosing the disease.

In part, this is because earlier versions of the test were not as accurate as current versions.

The test measures the percentage of glycated hemoglobin, or A1C, in the blood and provides an assessment of blood sugar levels over the previous two to three months.

Hemoglobin is a protein on red blood cells that carries oxygen in the blood. When blood sugar is too high it combines with hemoglobin.

The more excess glucose in the blood, the higher the percentage of A1C. Healthy adults without diabetes or prediabetes have an A1C of about 5%. Diabetes patients with very poorly controlled disease can have levels as high as 25%.

Under the new recommendations, people with A1C levels between 5.7% and 6.4% will be considered to have prediabetes and those with levels of 6.5% or higher will be considered to have diabetes.

Diabetes testing is recommended for:

• Any adult who is overweight or obese (BMI of 25 or greater) with one or more additional risk factor for diabetes including: having a family history of the disease, belonging to a high-risk ethnic group (African-American, Latino, Native American, Asian-American), having high blood pressure or a history of gestational diabetes.
• Anyone who is age 45 or older, regardless of risk factors.

Test Could Identify Millions

Buse says the new test could help identify millions of people with prediabetes who would otherwise not be tested for diabetes.

"I'm thinking of an overweight guy who is 40 years old who doesn't see the doctor unless he strains his back or is sick," he says.

Because conditions such as pain and infection can cause temporary elevations in blood sugar, this patient would probably not be tested for diabetes in this setting using the traditional blood glucose tests.

The new guidelines also call for patients with prediabetes to have access to programs designed to promote weight loss and lifestyle changes that could prevent the disease.

Third-party payers do not typically cover these programs but they can be highly effective for preventing diabetes, which is an expensive disease to treat if poorly managed, current ADA president for medicine and science Richard M. Bergenstal, MD, tells WebMD.

"Even modest weight loss and increases in activity can keep people with prediabetes from developing the disease," he says.

Recent studies suggest that overweight people who lose just 5% to 10% of their body weight and exercise as little as 30 minutes a day, a minimum of five days a week, can reduce their diabetes risk by close to 60%, Buse says.

SOURCES: American Diabetes Association: "Standards of Medical Care in Diabetes -- 2010," Diabetes Care, January 2010; vol 33: supplemental issue.

John Buse, MD, PhD, professor of medicine, chief of endocrinology, University of North Carolina, Chapel Hill; past president for medicine and science, American Diabetes Association.

Richard M. Bergenstal, MD, president for medicine and science, American Diabetes Association.

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