Q: I have Type 2 diabetes, and I check my blood sugar levels every day. Why do I need to have my HbA1c levels tested every few months?
A: Diabetes is marked by high levels of glucose (sugar) in the blood and urine. Without adequate treatment, diabetes can cause serious long-term complications. The key to preventing them is to control blood sugar -- to keep it close to the normal level.
In order to control your blood sugar levels, you need to know what they are.
When I was training in medicine, the only way a patient could do that on his or her own was to test the amount of sugar in the urine. Checking the sugar levels in the blood required a blood test and laboratory analysis.
Today, by sticking a finger to draw a drop of blood, people can test their blood sugar with a simple home machine: a glucose meter.
Home blood sugar testing machines are quite accurate. But, like a blood sugar test the doctor does, the result tells you what your blood sugar level is only at the moment the blood is tested. That's an important limitation, because blood sugar levels vary throughout the day.
When you eat, sugar levels rise. When you exercise, you burn off some of the sugar and lower blood levels. Stress and various medicines that you take also can affect blood sugar levels. So, of course, can medicines you take to lower your blood sugar.
That's where the hemoglobin A1c (HbA1c) test comes in. It's a "big picture" test. It is a way of estimating what your blood sugar levels have been, on average, day in and day out over the past two or thee months.
That's very important information, as your HbA1c value reveals whether your treatment program has kept your average blood sugar levels at normal or near-normal levels.
People with diabetes should aim for an HbA1c level of less than 7 percent. Daily blood sugar testing can help when you are adjusting your medications or deciding which dose of insulin to use.
Knowing your blood sugar level can also protect you from spells of low blood sugar (hypoglycemia), which can have dangerous complications of its own. And daily blood sugar testing also can spot times when your blood sugar level is getting dangerously high.
Your doctor will use the HbA1c test to spot trends in your blood sugar levels and head off complications. If your HbA1c levels are too high, your doctor should recommend starting medication. If you are already on medication, your doctor may adjust your dose or add another drug in order to achieve a lower HbA1c level at the next test.
Get your HbA1c levels tested every two to three months until you achieve the goal of less than 7 percent. Then, you can have your HbA1c levels tested every six months.
• Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com.