Lee Chung Horn
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  DIABETES MELLITUS

 

GLYCATED HEMOGLOBIN - THE TEST THAT NEVER FORGETS 

Because you have diabetes, you and your endocrinologist, diabetes educator and other members of your health care team work to keep your blood glucose at ideal levels. There are two powerful reasons to work for effective blood glucose control:

1 You will feel better

2 You may prevent or delay the start of diabetes complications like nerve, eye, kidney and blood vessel damage.

One way to keep track of your blood glucose changes is by testing your blood glucose at home. These tests tell you what your blood glucose level is at any one time.

But suppose you want to know how you have done overall. There's a test that does this. A glycated hemoglobin test (HbA1c) gives you a picture of your average blood glucose control for the past two to four months. This test must be done by a laboratory but the results give you a good idea of how well your diabetes treatment plan is working.

In some ways the glycated hemoglobin test is like a baseball player's season batting average. Both glycated hemoglobin and the batting average tell you about a person's overall blood glucose (or batting) success. Neither a single day's blood test results, or a single game's batting record, give the same big picture.

How it works

You know from the name that the test measures something called glycated hemoglobin. You may wonder what it has to do with your blood glucose control.

Hemoglobin is found inside red blood cells. Its job is to carry oxygen from the lungs to all the cells of the body. Hemoglobin like all proteins links up with sugars, such as glucose. When you have uncontrolled diabetes you have too much glucose in your bloodstream. This extra glucose enters your red blood cells and links up (or glycates) with molecules of hemoglobin.

The more excess glucose in your blood, the more hemoglobin gets glycated. It is possible to measure the percentage of glycated hemoglobin in the blood. The result is an overview of your average blood glucose control for the past few months.

How does the glycated hemoglobin test look backward?

Suppose your blood glucose was high last week. What happened? More glucose got hooked up with your hemoglobin. This week, your blood glucose is back under control. Still your red blood cells carry the "memory" of last week's high blood glucose in the form of more glycated hemoglobin. This 'record' changes as old red blood cells in your body die and new red blood cells (with fresh hemoglobin) replace them. The amount of glycated hemoglobin in your blood reflects average blood glucose control for the past two to four months, or the lifespan of a red blood cell.

In a person without diabetes, about 5% of all hemoglobin is glycated. A HbA1c level of more than 8% indicates unacceptable control. 7-8% indicates suboptimal control. A level of less than 7% is desirable. In bad cases, the HbA1c can go as high as 20%.  But while the glycated hemoglobin test is an important tool, it can't replace daily self-testing of blood glucose. Glycated hemoglobin tests don't measure your day-to-day control. You can't adjust your insulin on the basis of your glycated hemoglobin tests. 

Glycated hemoglobin tests can help:

Confirm self-testing results or blood test results by the doctor.

Judge whether a treatment plan is working.

Show you how healthy choices can make a difference in diabetes control.


 

Copyright of Lee Chung Horn Diabetes & Endocrinology 2009