A new test to diagnose diabetes, recommended earlier this year by the American Diabetes Association, may not work well in black Americans, according to new research.

The study, published in the Annals of Internal Medicine, shows that black and white Americans have different amounts of the blood component measured by the test.

That component, called hemoglobin A1c, is formed when blood sugar comes into contact with hemoglobin, the protein in red blood cells that make our blood red.

That means hemoglobin A1c can act like a dipstick for blood sugar, which is elevated in diabetics. Because too much blood sugar is harmful to our organs, an elevated level of the protein suggests a high risk of suffering diabetes-related complications, like kidney or eye disease.

While scientists knew that black people tended to have higher levels of hemoglobin A1c, most thought it was simply a matter of higher blood sugar levels.

But according to the new findings, based on a representative sample of Americans without diabetes, black people have consistently more hemoglobin A1c than whites, even when there is no difference in blood sugar, obesity and other factors.

Although the reason is not clear, the researchers say this limits the use of the proposed diabetes test in the U.S. The U.S. Preventive Services Task Force - an independent panel of medical experts appointed by the federal government - recommends adults with elevated blood pressure be screened for diabetes, but do not specify which test.

Currently, the commonly accepted standard is a blood test given after a high dose of sugar following an overnight fast.

However, Dr. Richard Bergenstal, president of medicine and science at the American Diabetes Association, said he did not think the association’s recommendations should be changed.

He pointed out that the difference found in the study, less than half a percent, was minor compared to the Association’s cut-off value for diagnosing diabetes. That value is set at 6.5 percent hemoglobin A1c, out of all of the hemoglobin in the blood.

“It’s significant only if you happen to be right on the edge,” he said. “Let’s not throw out a good test that can be used to identify people at risk.”

He said the study was important, but that we needed more research.

“I don’t think we are at the level of understanding yet to change the guidelines for blacks and whites,” he said.

SOURCE:  Annals of Internal Medicine, June 14, 2010.