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.