Beyond Blood Sugar: Testing A1c
Reviewed By Charlotte Grayson
What's your A1c? If you have diabetes and you don't know the answer, you should.
"The A1c [or glycated hemoglobin or HbA1c] is critical in the management of both type 1 and type 2 diabetes," says Fran Kaufman, MD, president of the American Diabetes Association. "It's a wonderful test."
Kaufman, who is also division head of endocrinology at the Children's Hospital Los Angeles, is not alone in her glowing assessment of the A1c. "The A1c test has been a revolutionary change in diabetes management," says David E. Goldstein, MD, chair of the NGSP steering committee, the organization that developed standards for A1c testing.
Despite enthusiastic reception by experts, the benefits of A1c testing are still not apparent to everyone. Not enough people with diabetes have their A1c tested regularly and, even when they do, many don't understand the results. In a survey conducted by the American Association of Diabetes Educators, only 24% of people with diabetes knew their A1c levels. Given the severe and life-threatening risks of diabetes -- such as heart disease and stroke -- that number is disturbingly low.
Everyone with diabetes is familiar with the standard, fasting blood-glucose test that is used to indicate your current blood sugar levels. The fasting test is the warhorse of diabetes management, and it helps you and your doctor see how your treatment is going.
But while the fasting test remains an important part of diabetes treatment, its weakness is that it is an indication of your glucose level only at the moment you take the test. A fasting blood sugar doesn't tell you anything about your blood-sugar levels the rest of the time.
The hemoglobin A1c test -- usually called the A1c -- fills this gap by testing your blood sugar in a different way. As your body processes blood sugar, small amounts of glucose naturally bond with hemoglobin, a protein in the red blood cells. What's significant is that the amount of glucose that combines with the hemoglobin is directly proportional to the total amount of glucose that is currently in your system.
As a result, the hemoglobin bonded with glucose (glycated hemoglobin, or A1c) can be used as an overall record of glucose levels for as long as the individual red blood cell lives, which is about two to three months. While a fasting test gives you an indication only of current glucose levels, the A1c gives you the big picture of what your average levels are over this whole two to three month period.
Getting a reading of overall blood glucose, instead of relying only on a series of fasting readings, has made a big difference in diabetes management.
Goldstein says that fasting-glucose tests alone were not a very good indicator of how well a person was doing in controlling his or her blood sugars. He says that he and other experts used to be surprised by patients who appeared to have good glycemic control -- based on fasting sugars -- but who would then suddenly develop serious complications.
"By checking the A1c, we don't see surprises like that anymore," Goldstein tells WebMD. "When we monitor people in the long term, we don't see people with great A1c levels developing classic complications of diabetes."
The test itself is simple and quick and thanks to the work of the NGSP (formerly the National Glycohemoglobin Standardization Program), more than 90% of all A1c tests are now standardized, meaning that the results from different labs should be comparable. Experts are not yet sure how often people with diabetes need to have their A1c tested, but the American Diabetes Association settled on a range of two to four times per year based on current evidence.
How Low Should it Be?
Experts agree that a normal A1c for someone without diabetes is between 4%-6%; anything above that should be considered a sign of diabetes.
But exactly where you should be on that scale is debated and the recommendations for target A1c levels vary. For instance, the American Diabetes Association recently changed its recommended A1c from under 8% to 7% or below. Meanwhile, the American Association of Clinical Endocrinologists (AACE) recommends an even lower number of less than 6.5%.
All of these different numbers might leave you a bit confused. However, the general rule is that the closer to a normal A1c a person can get, the better, provided that the glucose control is not so strict -- or tight, in medical terminology -- that it induces hypoglycemia, a level of blood sugar that is too low. Treatment almost always includes behavioral techniques, such as weight loss and exercise, and may include medications to lower blood sugar levels.
But it's important to know that not everyone can reach these goals. "I've been delighted with the number of patients I have with A1c levels in the low 6% area," says Paul Jellinger, MD, past president of the American Association of Endocrinologists. "But in some patients who have unstable blood sugar levels, you're content with 7.2% or 7.4%, since that's the best you can do."
Goldstein is somewhat doubtful of the new, lower targets. "I agree that people should strive for the lowest A1c possible," he says, "but most patients can't achieve either the ADA or the AACE goals with current therapies because they're so low. And I think that you have to be careful not to set a goal that most people can't attain."
So what's the upshot? Get your A1c tested regularly and consult with your doctor about what target you should set. In general, aim for below 6.5% or 7%, but understand that it may not always be possible to get there.
Doing it Yourself
At least one at-home test kit for A1c levels has been developed, and more are probably on the way. While it may be somewhat more convenient than trudging into the doctor's office, Goldstein and Kaufman are a little skeptical of their usefulness.
"If A1c levels were something that you had to monitor every few days, a home test would make more sense," says Goldstein. "But A1c is a long-term measure of blood sugars and you don't need to do it very often, maybe every few months. So why do people need to do it at home and why would doctors want them to?"
"I'm concerned about people doing these at home," Kaufman tells WebMD. "I don't want people to start doing A1c tests on their own and then thinking they can skip healthcare visits. It's not a substitute."
Instead, Kaufman and Goldstein recommend that A1c tests be administered in the doctor's office, where other indications -- such as blood pressure, cholesterol levels, and weight -- can also be checked. "People with diabetes need to be seeing their doctors regularly anyway," says Goldstein.
However, Goldstein does see at least one useful application of the home A1c test. "I think it might be good as a home-screening test, like a home pregnancy test," he says, "for people who haven't been diagnosed with diabetes but who are concerned about getting the disease."
Various health organizations have been stressing the importance of A1c in recent years. The U. S. Department of Health and Human Services partnered with the ADA to develop the "ABCs of Diabetes Program," encouraging regular monitoring of A1c, blood pressure, and cholesterol. More recently, the American Association of Diabetes Educators began the "Aim. Believe. Achieve. Diabetes A1c Initiative," a national educational campaign to raise awareness about the A1c test.
Given the importance of the A1c and the risks of diabetes, you must get your doctor to tell you what your A1c is and, if it's too high, what you can do to lower it. Experts stress the importance of aggressive management of diabetes, and you may have to push yourself and your doctor to achieve a better A1c level.
"There are still some doctors out there who don't understand what A1c targets should be or how to achieve them," says Kaufman. "If you've got a high A1c and your healthcare provider isn't helping you, it's time to get a consultation with somebody else."
Originally published March 17, 2003.
Medically updated June 18, 2004.
SOURCES: Thomas Buchanan, MD, director of the clinical research center at the Keck School of Medicine; professor of medicine at the University of Southern California; leader of the Troglitazone in Prevention of Diabetes (TRIPOD) study. Om Ganda, MD, associate clinical professor of medicine at Harvard Medical School; senior physician and director of the lipid clinic at the Joslin Diabetes Center; attending physician at Beth Israel-Deaconess Medical Center, Boston. David E. Goldstein, MD, chair of the NGSP steering committee; professor of child health and principal investigator at the health sciences center at the University of Missouri School of Medicine. Paul Jellinger, MD, past president of the American Association of Clinical Endocrinologists (AACE); clinical professor in the department of medicine at the University of Miami School of Medicine. Fran Kaufman, MD, president of the American Diabetes Association (ADA); head of the division of endocrinology and metabolism and director of the comprehensive childhood diabetes center at the Children's Hospital in Los Angeles; professor of pediatrics at the Keck School of Medicine. David M. Nathan, MD, director of the general clinical research center and of the diabetes center at Massachusetts General Hospital; professor of medicine at Harvard Medical School; chairman of the Diabetes Prevention Project (DPP).
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