By JoAnne Allen
WASHINGTON (Reuters) - A test that shows blood sugar levels over a span of several weeks is not only the best way to diagnose diabetes but also may be better at identifying who is at risk of getting diabetes than standard blood sugar tests, researchers said on Wednesday.
In a study involving more than 11,000 people with no history of diabetes, the hemoglobin A1c test more accurately identified people who later developed diabetes than the glucose fasting test, which measures blood sugar levels at one point in time.
The A1c test was also a better predictor of risk for stroke, heart disease and death from diabetes, the researchers reported in the New England Journal of Medicine.
They found that people who had A1c levels at 6 percent or greater were at higher risk for developing diabetes.
"A1c has significant advantages over fasting glucose," Dr. Elizabeth Selvin of Johns Hopkins University in Baltimore, who led the study, said in a statement.
Blood sugar levels can vary from day to day and hour to hour.
The A1c test is more reliable, repeatable and allows doctors to track average glucose levels over time. Levels are not as affected by stress and illness, and patients do not have to fast before the test, the researchers said.
In January, the American Diabetes Association recommended the A1c test for diabetes screening and to identify people who may be at risk of developing the disease. Fasting glucose had been the standard measure in the United States for decades.
In the study, Selvin and colleagues examined stored blood samples from 11,092 black and white middle-aged adults without diabetes. The samples were collected between 1990 and 1992.
They compared the A1c test to the fasting glucose test to identify people at high risk for diabetes, heart disease, stroke and death.
During 15 years of follow-up, 2,251 people were diagnosed with diabetes; 1,198 had heart disease, 358 had strokes and 1,447 died, the researchers said.
A1c levels between 5.0 to 5.5 percent are considered normal. With each incremental A1c increase, the researchers found the incidence of diabetes rose.
People with levels between 6 and 6.5 percent were nine times more likely than those at the normal range to develop diabetes.
There are currently 9 million Americans who are diabetic but are undiagnosed, according to the study.
"These data... can help us interpret A1c values in clinical practice and help identify people who need treatment the most," Selvin said.
Diabetes develops when the body loses its ability to use insulin effectively. Blood sugar levels rise, in turn causing complications including heart disease, blindness and kidney failure.
About 24 million Americans have diabetes, according to the U.S. Centers for Disease Control and Prevention. Diabetes costs the United States about $132 billion per year in disability, loss productivity and premature death.