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Glycohemoglobin (HbA1c, A1c)
Test Overview
Glycohemoglobin is a blood test that checks the amount of sugar (glucose)
bound to
hemoglobin. Normally, only a small percentage of
hemoglobin in the blood (4% to 6%) has glucose bound to it. People who have
diabetes or other conditions that increase their blood
glucose levels have more glycohemoglobin than normal.
The
glycohemoglobin A1c test checks the long-term control of blood glucose levels
in people with diabetes. Most doctors think the glycohemoglobin A1c level is
the best way to check how well a person is controlling his or her diabetes.
A home blood glucose test measures the level of blood glucose
only at that moment. Blood glucose levels change during the day because of
diet, exercise, and the level of insulin in the blood.
It is
useful for a diabetic to have information about the long-term control of blood
sugar levels. The glycohemoglobin test is one blood sample every 3 to 4 months,
and the test does not change with any recent changes in diet, exercise, or
medicines.
Glucose binds to hemoglobin in red blood cells at a
steady rate. Since red blood cells last 3 to 4 months, the glycohemoglobin A1c
test shows how much glucose is in the
plasma part of blood. This test shows how well your
diabetes has been controlled in the last 2 to 3 months and whether your
diabetes medicine needs to be changed.
The A1c level can also help
your doctor see how big your risk is of developing problems from diabetes, such
as kidney failure, vision problems, and leg or foot numbness. The lower your
A1c level, the lower your chance for problems.
Why It Is Done
This test is done to check your
treatment for diabetes.
How To Prepare
You do not need to stop eating before
you have a glycohemoglobin test. This test can be done any time during the day,
even after a meal.
How It Is Done
The health professional taking a sample
of your blood will:
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
alcohol.
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
blood.
- Remove the band from your arm when enough blood is
collected.
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure on the site and then put on a
bandage.
How It Feels
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch.
Risks
Blood test
There is very little chance of a
problem from having blood sample taken from a vein.
- You may get a small bruise at the site. You
can lower the chance of bruising by keeping pressure on the site for several
minutes.
- In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.
- Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.
Results
Glycohemoglobin is a blood test that
checks the amount of sugar (glucose) bound to
hemoglobin. The result is shown as a percentage and
may be compared with a number value. Your A1c level may be reported without a
total glycohemoglobin value. Your doctor will have your test results in 1 to 2
days.
Normal
Normal values vary from lab to lab,
depending on the test method used.
Glycohemoglobin (GHb)
| Glycohemoglobin
A1c: |
4.5%–5.7%
|
| Total
glycohemoglobin: |
5.3%–7.5%
|
- The American Diabetes Association (ADA) recommends
that people with diabetes have an A1c level less than 7%. If levels are greater
than 8%, the ADA recommends that diabetes treatment be looked at and changed as
needed.
Comparison of A1c and plasma glucose
levels
| A1c % | Average
plasma glucose (mg/dL) | Average plasma glucose (mmol/L) |
| 6% | 135 | 7.5 |
| 7% | 170 | 9.5 |
| 8% | 205 | 11.5 |
| 9% | 240 | 13.5 |
| 10% | 275 | 15.5 |
| 11% | 310 | 17.5 |
| 12% | 345 | 19.5 |
The American Diabetes Association has the following
recommendations for children and adolescents with diabetes:1
A1c recommendations for children and
teens
| Age | A1c % |
| Children younger than 6
years old | 7.5–8.5% |
| Children ages 6 to 12
years old | Less than 8% |
| Teens ages 13 to 19
years old | Less than 7.5% |
High values
A glycohemoglobin A1c level above 8%
means that your diabetes has been poorly controlled over the last 2 to 3
months.
Some medical conditions can increase A1c levels, but the
results may still be within a normal range. These conditions include
Cushing's syndrome,
pheochromocytoma, and
polycystic ovary syndrome (PCOS).
Corticosteroid treatment increases the A1c
level.
A1c levels may be higher in children and adolescents with
diabetes.
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
- Having severe blood loss or a blood transfusion
in the last 3 months.
- Having certain medical conditions, such as
sickle cell anemia,
hemolytic anemia, some types of
thalassemia, and severe kidney
disease.
- Having your spleen taken out. This changes the normal life
cycle of
red blood cells and A1c levels.
What To Think About
- If you have
diabetes, your doctor may recommend that you have a
glycohemoglobin test every 3 to 6 months, depending on your type of diabetes
and how well it is controlled. For most people, A1c is measured 3 to 4 times a
year.
- The glycohemoglobin test does not replace the need for other
regular blood glucose tests, including checking your blood sugar at home and a
regular blood glucose test. For more information, see the medical test
Home Blood Glucose Test and
Blood Glucose.
- Many people with diabetes
have high blood sugars at times when they would not be checking their blood
sugar, such as after meals or during the night. Glycohemoglobin A1c may show
these periods of high blood sugar that would not be found by a home blood
glucose test.
- Some people who develop diabetes have normal
glycohemoglobin tests early in the course of their
disease.
- Glycohemoglobin levels can be normal in some people who
have untreated diabetes and certain medical conditions, such as sickle cell
anemia, hemolytic anemia, severe kidney disease, or pregnancy.
- If
you have diabetes, having a high glycohemoglobin level increases your chances
of having other problems. Lowering your glycohemoglobin levels can help delay
or prevent problems, such as serious nerve, kidney, and eye damage.
- Glycohemoglobin levels are not useful for finding low blood sugar
(hypoglycemia).
References
Citations
-
American Diabetes Association (2005). Care of children
and adolescents with type 1 diabetes. Diabetes Care, 28(1): 186–212.
Other Works Consulted
-
American Diabetes Association (2008). Standards of
medical care in diabetes. Clinical Practice Recommendations 2008.
Diabetes Care, 31(Suppl 1): S3–S110.
-
Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed.
Philadelphia: Saunders.
-
Fischbach FT, Dunning MB III, eds. (2004).
Manual of Laboratory and Diagnostic Tests, 7th ed.
Philadelphia: Lippincott Williams and Wilkins.
-
Pagana KD, Pagana TJ (2006). Mosby’s
Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis:
Mosby.
Credits
| Author | Caroline Rea, RN, BS, MS |
| Editor | Maria Essig |
| Associate Editor | Tracy Landauer |
| Primary Medical Reviewer | Martin Gabica, MD - Family Medicine |
| Specialist Medical Reviewer | David C.W. Lau, MD, PhD, FRCPC - Endocrinology & Metabolism |
| Last Updated | May 29, 2008 |
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| Author: | Caroline Rea, RN, BS, MS | Last Updated: May 29, 2008 |
| Medical Review: | Martin Gabica, MD - Family Medicine
David C.W. Lau, MD, PhD, FRCPC - Endocrinology & Metabolism |
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