Glycosylated Hemoglobin Testing

Research has proven that good control of diabetes is the best way to prevent or delay complications of the disease, complications that include heart disease, blindness, nerve damage and kidney damage. While your daily blood testing tells you how your blood sugar is doing right then, allowing you to make necessary changes in medicine, food and exercise, it doesnít give you a picture of your long-term diabetes management success. To do that, there is glycosylated hemoglobin testing.

The glycosylated hemoglobin test, or Hemoglobin A1c (HbA1c), is a test used to give you and your doctor the most accurate picture of your overall diabetes control. Hereís how it works.

Sugar that is not used for energy is left in the blood, where it attaches itself to the hemoglobin, which is the part of the red blood cell that carries oxygen, in a process called glycosylation. The more glucose there is in the bloodstream, the more glucose builds up in the cells. This binding of sugar to molecules in cells is one way diabetes causes physical damage and health problems.

The HbA1c test measures the amount of sugar that is attached to the hemoglobin in red blood cells, with results given as a percentage. Athough different laboratories may use diffeent testing methods, the percentage that occurs in people without diabetes is usually about six percent. Because red blood cells live in the bloodstream for about four months, the HbA1c test shows the average blood sugar for the past several months, similar to the way the batting average of a baseball player is calculated over a period of time.

Unlike your regular blood sugar test, the HbA1c test is not affected by short-term changes. So even though you may have had high blood sugar on occasion, a good glycosylated hemoglobin result can show that, overall, you are doing a good job of controlling your diabetes. (Just like a baseball player can strike out several times over a few weeks, and still be a champion hitter.)

The chart below shows the average daily blood glucose levels for four different HbA1c values.

HbA1c Value Average daily blood glucose level over past three months


120 mg/dl (pretty good)


180 mg/dl (not too bad)


240 mg/dl (not good)


330 mg/dl (dangerous)

The HbA1c test should be done every three to six months, depending on your treatment program and level of control. Itís a good idea to discuss the HbA1c test with your doctor or diabetes educator, and ask what the normal range for the test is at the laboratory your doctor uses. Then, when you find out your HbA1c value, youíll know whether you are on target, or whether you need to work with your physician or diabetes educator on better control of your diabetes.

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