New Uses for Old-Line Diabetes Monitoring Test: Screening and Diagnosis

A blood test currently used as the gold standard for monitoring people already under care for diabetes may have far wider use in identifying millions with undetected diabetes, a team led by a Johns Hopkins physician suggests.

The hemoglobin A1c test (HbA1c), based on a blood sample, is widely used to keep tabs on how well confirmed diabetics keep their blood sugar, or glucose, in check by showing how much glucose red blood cells have been exposed to for the past 120 days, the average lifespan of these cells.

"The test is a measure of long-term glucose control, but doctors don't typically use it to screen for or diagnose the disease, " says Christopher Saudek, M.D., professor of endocrinology and metabolism at the Johns Hopkins University School of Medicine and director of the Johns Hopkins Comprehensive Diabetes Center. "There's reason to believe it could help identify many of the estimated six million people in the U.S. who have diabetes but don't know it," he adds. The current screening and diagnostic tests measure only the amount of sugar present at the moment that blood sample is taken. Consequently, Saudek says, these tests are accurate only if patients fast for at least 10 hours before the test because glucose concentrations can vary greatly depending on a person's recent meals.

Even then, explains Saudek, the tests miss a significant portion of people who have diabetes or are at high risk to develop the disease since glucose also varies depending on a person's diet and exercise regimen for several days leading up to the blood draw.

"If a patient is scheduled for a physical, he or she may 'tune up' by changing their regimen for a few days and throw off their test results, causing doctors to miss the patient's usual pattern of high blood sugar," he says.

In a consensus statement published in the July Journal of Clinical Endocrinology and Metabolism, Saudek and his colleagues conclude that the HbA1c test should be used as a front-line method for identifying patients with diabetes, especially for those at high risk for the disease. Since the test does not require fasting and isn't affected by short-term changes in diet and exercise, the HbA1c test has significant advantages to current testing methods.

The consensus was reached by a group of diabetologists, pathologists and internists seeking to improve detection methods because of the serious consequences of untreated diabetes for patients and public health. They met recently in Chicago with financial support from Metrika Inc., a major manufacturer of diabetes testing equipment. The panel deliberations and manuscript preparation were made independently of the sponsor, according to its members.

After reviewing relevant published studies and available tests, the national panel recommended that individuals who score at least 6 percent on an HbA1c test may have or be at risk for diabetes and should be tracked with additional glucose or HbA1c tests. Those who score between 6.5 percent or above, if confirmed, should be considered to have diabetes.

"This is a first step towards changing medical practice," notes Saudek, and "could greatly enhance how well we're able to identify people with diabetes."

Others who contributed to the consensus statement include William H. Herman of the University of Michigan School of Medicine, David B. Sacks of Brigham & Women's Hospital and Harvard Medical School, Richard M. Bergenstal of the International Diabetes Center, David Edelman of Durham Veterans Administration Medical Center and Duke University, and Mayer B. Davidson of Charles R. Drew University.