June 23, 2013 | by Nicole White
One of the most commonly used diabetes diagnostic tests – popular with patients and physicians because it requires no fasting and no drinking of sickly sweet liquids – is actually unable to detect the disease in most patients, according to new City of Hope research. In fact, it picks up only about 25 percent of cases identified by other blood tests, scientists have found.
The HbA1C, or hemoglobin A1c test, was accepted as a measure for diabetes diagnosis by the American Diabetes Association and World Health Organization in 2010 and 2011. The simple blood test, which checks for the percentage of glycated hemoglobin in the bloodstream, has grown in popularity because it doesn’t require patients to fast, unlike the two other most common diabetes tests. However, that convenience comes at a high price, researchers found.
“If we rely on the A1C test for diagnosis, we will miss a lot of patients,” said Raynald Samoa, M.D., assistant professor in the Division of Molecular Diabetes Researchat City of Hope and a lead author on the study. “If we want to diagnose diabetes earlier, so we can intervene earlier and potentially prevent diabetic complications from developing, the other tests are better tools.
Diabetes, including type 1 and type 2, affects 25.8 million people, or 8.3 percent of the U.S. population, according to the federal Centers for Disease Control and Prevention. This includes an estimated 7 million undiagnosed cases of the disease. Diabetes is the seventh-leading cause of death in the United States; the leading cause of kidney failure, nontraumatic lower-limb amputations and new cases of adult blindness; and a major cause of heart disease and stroke.
The A1c test to detect diabetes assesses the percentage of hemoglobin that is coated with sugar, known as glycated hemoglobin. A finding of 6.5 percent or more is considered positive for diabetes. The two other common tests measure glucose levels in the blood, both of which require patients to fast for eight hours. Additionally, the two-hour plasma glucose test requires patients to drink a sweet liquid containing a certain amount of glucose, and have multiple blood draws.
Although the plasma glucose tests are more time-consuming and inconvenient for patients, the City of Hope studies found they are more sensitive and identify more cases of diabetes, said Ken Chiu, M.D., professor in the Department of Clinical Diabetes, Endocrinology and Metabolism at City of Hope and a senior author of the studies. The findings were presented separate abstracts at The Endocrine Society meeting in San Francisco and the American Diabetes Association’s scientific session in Chicago.
City of Hope researchers conducted a database analysis of 5,764 patients who had received all three diagnostic tests. The A1c hemoglobin test picked up only about 25 percent of the cases identified by the other two tests. Those most likely to be missed by the A1c test included older people, women, lean people and nonsmokers. Researchers pointed out that the A1c remains a valuable tool for management of diabetes, helping doctors determine whether their patients’ disease is under control.
“The take-home here is that A1c is a good tool to guide us in the treatment of diabetes, as we have clear goals to get the A1c down to less than 7 percent,” Chiu said. “Although it’s a simple test to do, and no preparation is required, the sensitivity is much lower compared to the other two tests available. In order to make diagnoses earlier, those are better tools.”