Hemoglobin A1c Not Reliable in Diagnosing Type 2 Diabetes

    The test that doctors most often rely on to detect a person’s risk for prediabetes and type 2 diabetes—the hemoglobin A1c (A1c) blood test—too often delivers a poor reading, thereby missing the diagnosis in nearly three out of four at-risk individuals,1 according to research presented at the Endocrine Society meeting in New Orleans, Louisiana.The investigators compared the accuracy of the A1c test with the other screening method used to assess patients’ risk of diabetes—the oral glucose tolerance test (OGTT)—to arrive at this startling conclusion.1

     The common use of the hemoglobin A1c test to screen for prediabetes and type 2 diabetes should be skipped in place of more reliable tests. "The A1c missed almost 73% of the people with diabetes in comparison to the oral glucose tolerance test," says  Chang Villacreses, An Endocrinologist.

                   The A1c lab value represents a look back at average blood glucose levels over the previous three months. It has been commonly used to detect diabetes for the last decade. Unlike other tests, no fasting is needed before you have blood drawn to assess your A1c level, making it more convenient for people.Since the fasting blood test requires a person to fast, the OGTT measures the body's response to sugar; it requires a person to fast overnight. First, blood is taken, then the person drinks a sugary drink. Blood is taken again two hours later.

The guidelines for diagnosis and treatment of type 2 diabetes from the American Diabetes Association (ADA) already advise against relying solely on A1c,3 she says. “While the American Diabetes Association guidelines specify that diabetes can be diagnosed based on fasting plasma glucose (FPG), the OGTT, or the A1c, our findings confirm that reliance on A1c remains the least reliable method for assessing diabetes risk.”

The choice of which tests to use is of course left to the discretion of the physician, Dr. Villacreses says. "We wanted to bring this up to emphasize the gap [in the accuracy of detection," she says, between the A1c and the other tests.

"The guidelines also state that if the A1c is normal and there is still a suspicion of prediabetes or diabetes, doctors are advised to do the OGTT anyway," she says. So an A1c can be done so long as you are then advised to have another test to check your blood sugar levels if there is any concern regarding your risks.

To fully understand the reason that problems arise with the reliability of the A1c test, Dr. Christofides explains that when circulating glucose builds up in the blood, it binds to the hemoglobin molecule in the red blood cell, and the A1c measures how much glucose is bound.

As the differences found among different patient populations, she says that genetic mutations are more likely to occur in certain ethnicities, which alter the way the glucose binds to the hemoglobin molecule—thereby giving false readings more often. African Americans, for instance, carry a variant form of a gene for the sickle cell anemia that is involved in abnormal binding of blood glucose, she says, so the A1c test is artificially lower than expected in these patients.

What Does This Mean for People Wondering About Their Diabetes Risk
For individuals who haven’t received a diagnosis of diabetes, Dr. Villacreses says, one important lesson from these fidings is that ''you should not feel 100% reassured if your A1c number is less than 6.5% that you are do not have diabetes.” A test result that is greater than 6.4% defines the beginning of diabetes, so you may have prediabetes or have already progressed to type 2 diabetes.

The sooner you receive a diagnosis regarding your diabetes status, the earlier treatment can begin. This is important because by understanding your risks, and making the necessary lifestyle changes, you can prevent prediabetes from progressing or even reverse the type 2 diabetes.

In addition, she says, patients should feel comfortable asking their doctor about the choice of tests and indicate your desire to skip the A1c, and have one of the other more reliable screening methods, while more time consuming, to determine if you are at risk for pre-diabetes or diabetes.