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The ABCs of the A1C

By David Mendosa

Last Update: November 17, 2006

The hemoglobin A1C test (also called just the A1C) is a simple lab test that shows the average amount of glucose that has been in a person’s blood during the past three months.

The hemoglobin A1C test shows if a person’s blood glucose is close to normal or too high. It is the best test for a health care provider to tell if a person’a blood glucose is under control.

What does this test measure?

Glucose in the bloodstream can become attached to the hemoglobin (the part of the cell that carries oxygen) in red blood cells. This process is called glycosylation (pronounced gli-kos-a-LAY-shen). Once the glucose is attached, it stays there for the life of the red blood cell, which is about 120 days. The higher the level of blood glucose, the more glucose attaches to red blood cells. The hemoglobin A1C test measures the amount of glucose sticking to the hemoglobin in the red blood cells. Results are given in percentages.

Why do more people need to know about this test?

The findings of a major diabetes study, the Diabetes Control and Complications Trial have shown just how important the hemoglobin A1C test is. The study showed that lowering the hemoglobin A1C number can delay or prevent the development of serious eye, kidney, and nerve disease in people with diabetes. The study also showed that lowering hemoglobin A1C levels by any amount improves a person’s chances of staying healthy.

When should this test be done?

All people with diabetes should have a hemoglobin A1C test at least twice a year. People with diabetes should get the test more often if their blood glucose stays too high or if their health care provider makes any change in their treatment plan.

How is the hemoglobin A1C test done?

This test is usually done in a health care provider’s office. To do the test, a small sample of blood is taken. The blood sample is sent to a laboratory for testing, and the laboratory sends the results to the patient¬¨√≠s health care provider.

Where does self-monitoring of blood glucose fit in?

Self-monitoring of blood glucose is also very important. A finger-stick test using a blood glucose meter measures the actual level of glucose in the blood at the time of the test. The meter reading is reported in milligrams per deciliter (mg/dl).

Self-monitoring of blood glucose helps people with diabetes see how food, physical activity, and diabetes medicine affect their blood glucose. The readings from these tests can help people with diabetes manage their disease day by day or even hour by hour. The readings can also tell them when their blood glucose is too low or too high, so they can work with their health care provider to change their treatment plan.

All people with diabetes need regular hemoglobin A1C tests. Most people with diabetes also need to self-monitor their blood glucose to get a complete picture of blood glucose control. Self-monitoring blood glucose gives a snapshot of control at the time of the test, while the hemoglobin A1C test gives the big picture of control during the past three months. Together, these tests tell a patient and his or her health care provider whether the patient’s blood glucose is under control.

What does a hemoglobin A1c test result mean?

The hemoglobin A1C goal for people with diabetes is less than 7 percent. The DCCT findings showed that people with diabetes who keep their hemoglobin A1C levels close to 7 percent have a much better chance of delaying or preventing diabetes problems that affect the eyes, kidneys, and nerves than people with hemoglobin A1C levels 8 percent or higher. A change in treatment is almost always needed if a person’s hemoglobin A1C is over 8 percent. But, if people with diabetes can lower their hemoglobin A1C number by any amount, they will improve their chances of staying healthy.

How does the hemoglobin A1C relate to readings from self-monitoring of blood glucose?

People with high daily blood glucose readings most of the time will usually have a high hemoglobin A1C test result. To maintain a hemoglobin A1C level less than 7 percent means that the blood glucose should rarely go above 150 mg/dl on any self-monitoring blood glucose test performed before meals during the previous 3 months. The blood sugar also should not drop below 60 to 70 mg/dl, or low blood glucosoe occurs.

How can people with diabetes keep their hemoglobin A1C at less than 7 percent?

Staying in control of diabetes over a prolonged period of time requires following a recommended meal plan, sticking to a physical activity program, taking prescribed diabetes medicines, self-monitoring of blood glucose, and consulting a health care provider often. When a patient has a high hemoglobin A1C test result, a health care provider can work with the patient to identify what is causing high blood glucose by examining the patient’s record of self-monitoring blood glucose. Common causes of high blood glucose include eating too much food or eating the wrong foods, lack of physical activity, stress, a need to change medicines, and infection or illness. By finding the source of the problem, a health care provider can decide if and how to change a patient’s treatment plan to meet the hemoglobin A1C goal of less than 7 percent.

How can people with diabetes use their hemoglobin A1C test results?

When people with diabetes know the results from their hemoglobin A1C test, they can take an active role in their diabetes management. A high hemoglobin A1C is one that is greater than 8 percent. People with diabetes who have a test result that is greater than 8 percent need to work with their health care provider to change their treatment plan.

A hemoglobin A1C test result that is close to normal is one that is less than 7 percent. When people with diabetes have a test result that is less than 7 percent, their treatment plan is probably working and it is likely that their blood sugar is under good control.

From the U.S. Veterans Administration web page

David Mendosa is a freelance journalist and consultant specializing in diabetes and lives in Boulder, Colorado. When he was diagnosed with type 2 diabetes in February 1994, he began to write entirely about that condition. His articles and columns have appeared in many of the major diabetes magazines and websites. His own website, David Mendosa’s Diabetes Directory, established in 1995, was one of the first and is now one of the largest with that focus. Every month he also publishes an online newsletter called “Diabetes Update.” Twice weekly he writes for his blog at He is a coauthor of The New Glucose Revolution: What Makes My Blood Glucose Go Up...And Down? (New York: Marlowe & Co., July 2006, and other publishers in the U.K., Australia, Taiwan, Vietnam, and Italy).

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