The HbA1c test can corroborate the daily blood glucose measurements you take or they can signal the need for a closer look at your therapy. A logbook full of blood glucose results that are in your target range and an HbA1c of 6.5% can leave you and your physician confident that your treatment is going well. However, if you only check your fasting blood glucose once a day and usually find it around 120 mg/dl yet your HbA1c is above 8%, you can be sure your blood glucose is much higher than 120 mg/dl at other times of the day. You will need to work with your health-care team to figure out when and why your highs are occurring. You may be encouraged to check your blood glucose levels more frequently as you and your team review your meal plan, physical activity levels, and medicines. Even people who monitor several times a day with few to no high results may be surprised to find they have a high HbA1c. In such cases, a little detective work might uncover a simple lab or meter error or the need to make changes in your meal plan, the timing of your blood glucose checks, or your blood glucose meter technique.
Who pays? Every health insurance and managed-care company has its own policies, so you’ll need to check your plan for specifics. However, most companies and Medicare cover the costs of HbA1c tests.
Most variations tend to occur in the number of tests covered per year and who runs the tests. Some plans allow quarterly tests while others cover 10 or more per year. Several devices have been approved by the U.S. Food and Drug Administration for giving HbA1c results right in a doctor’s office (called point-of-service testing) or even at home. Although some physicians use the office-based test and like that they can give people feedback about their results at the time of an office visit, some insurers do not cover these tests and may require physicians to send your blood sample to an approved laboratory. In such cases, a physician may have you make another appointment to go over the results or may call you when results come in. Coverage of home HbA1c tests is variable, and although such tests can be as accurate as any other lab test, they should not be used as a substitute for a regular visit with your physician.
Risks. For people with diabetes, especially those who use insulin, the main risk in trying to achieve tight control is low blood glucose levels (hypoglycemia). In the DCCT, people in the intensive-control group had three times the risk of hypoglycemia as people in the conventional-treatment group. Severe hypoglycemia can result in altered consciousness, coma, or convulsions; impaired neuropsychological or intellectual function in children; or strokes or heart attacks in older adults.
For some people, the risk of severe hypoglycemia may necessitate higher target blood glucose levels. For others, hypoglycemia is a risk that can be managed by being more aware of when lows can occur, by learning how to treat them effectively, and by reversing any hypoglycemia unawareness (the inability to sense the physical and mental side effects of low blood glucose) by setting temporary, higher blood glucose targets.
HbA1c error. Several medical conditions can affect the HbA1c test result, including anemia, sickle cell disease (and sickle cell trait), and chronic kidney disease. Simple lab error is a possibility, too. Because HbA1c results are based on hemoglobin levels, anything that affects hemoglobin or the life of red blood cells can affect the HbA1c result. Shortened life spans of red blood cells, such as can happen in people with most forms of anemia or when recovering from blood loss, can falsely lower one’s HbA1c result because the red blood cells have less time to interact and bind with glucose molecules. Iron-deficiency anemia and some forms of genetic abnormalities of hemoglobin may falsely elevate HbA1c results. High levels of vitamins C and E in the blood may interfere with glycation — falsely lowering results.