Glycated Hemoglobin
The test that never
forgets Because
you have diabetes, you and your doctor, 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:
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've
done overall. There's a test that can help. A glycated hemoglobin test
gives you a picture of your average blood glucose control for the past
three 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,
nor 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 carrying oxygen from the lungs to all the cells of the
body. Hemoglobin, like all proteins, links up with sugars, such as
glucose. You know that 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. Thanks for
the Memories
How
does the glycated hemoglobin test look backward? Suppose your blood
glucose was high last week. What happened? More glucose hooked up with
your hemoglobin (glycated). 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 three to four months, or the
lifespan of a red blood cell. In a person who does not have diabetes,
about 5 percent of all hemoglobin is glycated. For someone with diabetes
and high blood glucose levels, the glycated hemoglobin level is higher
than normal. How high the glycated hemoglobin level
rises depends on what the average blood glucose level was during the past
weeks and months. Levels can range from normal to as high as 25 percent if
diabetes is badly out of control for a long time. You should have had your glycated
hemoglobin level measured when your diabetes was diagnosed or when
treatment for diabetes was started. If you use insulin to treat your type
1 or type 2 diabetes, you should have the test four times a year. Twice a year is enough for people with
type 2 diabetes who don't use insulin. In some cases, such as pregnancy, a
doctor may test more often. How Does
It Help Diabetes Control?
How
can your glycated hemoglobin test results help your control? Here are two
examples. Bob D., 49 years old, has type 2
diabetes. For the past seven years, he and his doctor have worked to
control his blood glucose levels with diet and diabetes pills. Recently, Bob's control has been
getting worse. His doctor said that Bob might have to start insulin shots.
But first, they agreed that Bob would try an exercise program to improve
control. That was four months ago. Bob stuck to
his exercise plan. Last week, when the doctor checked Bob's blood glucose
it was near the normal range. But the doctor knew a single blood test only
showed Bob's control at that time. It didn't say much about Bob's overall
blood glucose control. The doctor sent a sample of Bob's blood
to the lab for a glycated hemoglobin test. The test results would tell how
well Bob's blood glucose had been controlled, on average, for the past few
months. The glycated hemoglobin test showed
that Bob's control had improved. With the glycated hemoglobin results, Bob
and the doctor had proof that the exercise program was working. The test
results also helped Bob know that he could make a difference in his
glucose control. The glycated hemoglobin test can also
help someone with type 1 diabetes. Nine-year-old Lisa J. and her parents
were proud that she could do her own insulin shots and urine tests. Her
doctor advised her to begin a routine of two shots a day and to test her
blood glucose as well. Lisa kept records of all her test
results. Most were close to the ideal range. But at her next checkup, the
doctor tested her blood and found her blood glucose level was high. The
doctor sent a sample of Lisa's blood for a glycated hemoglobin test. The
results showed that Lisa's blood glucose control had in fact been poor for
the last few months. Lisa's doctor asked Lisa to do a blood
test. To the doctor's surprise, Lisa turned on the timer of her meter
before pricking her finger and putting the blood drop on the test strip.
The doctor explained to Lisa and her parents that the way Lisa was testing
was probably causing the blood glucose test errors. With time and more accurate test
results, Lisa and her parents got better at using her test results to keep
food, insulin, and exercise in balance. At later checkups, her blood
glucose records and the glycated hemoglobin test results showed good news
about her control. Glycated hemoglobin
tests can help
Test
Limits
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. That's why your blood glucose tests and
your test log are so important to staying in effective control. The glycated hemoglobin test must be
done in a lab. It is important to know that different labs measure
glycated hemoglobin in different ways. If you sent one sample of your blood to
four different labs, you might get back four different test results. For example, a 9 at one lab might mean
that blood glucose levels have been in the near normal range. At a second
lab, a 9 might be a sign that, on average, blood glucose was high. This
doesn't mean that any of the results are wrong. It does mean that what
your results say depends on the way the lab does the test. Talk to your doctor about your glycated
hemoglobin test results. Know that if you change doctors or your doctor
changes labs, your test numbers may need to be 'read' differently. The glycated hemoglobin test alone is
not enough to measure good blood glucose control. But it is good resource
to use along with your daily tests to work for the best possible control. For other related materials visit the
American Diabetes Association's Book Store or follow the hyperlinks to
related materials: Complete Guide to Diabetes,
The Uncomplicated Guide to Diabetes Complications, Type
2 Diabetes: Your Healthy Living Guide, or The
Take-Charge Guide to Type 1 Diabetes. Copyright © 1999 American Diabetes
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