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Glycohemoglobin

(Hemoglobin A1c; HbA1c; Glycosylated Hemoglobin; Hemoglobin—Glycosylated; A1C; GHb; Diabetic Control Index)

What Is Glycohemoglobin?

When glucose sticks to a part of red blood cells (RBCs) it is called glycohemoglobin. Glucose is the body's fuel source that we get from food. It can build up on a part of RBCs when glucose levels in the blood are too high. The more glucose in the blood, the thicker the coating on red blood cell part will be. RBCs last 3 months. Glycohemoglobin will show average glucose levels in the blood over the last 3 months.

Reason for the Test

Glycohemoglobin levels are higher in people with certain health problems such as diabetes. An HbA1c test may be done:

  • To screen people at high risk for diabetes.
  • To diagnose diabetes in people with symptoms.
  • To keep track of diabetes—HbA1c tests are done regularly to check long-term control of blood glucose in people with diabetes. It can tell how well a person is controlling their diabetes.
  • To track or diagnoses other health problems including kidney or blood problems.
  • To see if treatment is working the way it is supposed to.

Type of Sample Taken

A blood sample is taken from a vein in the arm. Or, a small drop of blood may be taken from a fingerstick.

Prior to Collecting the Sample

You may need to fast before the test. Your doctor will tell you if you need to take this step.

During the Sample Collection

You will be asked to sit. An area inside your elbow will be cleaned. A large band will be tied around your arm. The needle will then be inserted into a vein. A tube will collect the blood from the needle. The band on your arm will be removed. Once all the blood is collected, the needle will be removed. Some gauze will be placed over the site to help stop bleeding. You may also be given a bandage to place over the site. The process takes about 5 to 10 minutes.

For a fingerstick, a small tool pricks your fingertip. A few drops of blood are taken and placed in a small tube. Cotton or a bandage is used to stop the bleeding.

After Collecting the Sample

After the blood sample is taken, you may need to stay seated for 10 to 15 minutes. If you are lightheaded, you may need to stay seated longer. When you feel better, you can leave.

A bit of blood may ooze from the vein beneath the skin. It will cause a bruise. Firm pressure over the site after the needle is removed will decrease the chance of a bruise. A bruise will usually fade in a day or 2.

Call your doctor right away if you have redness, swelling, lasting bleeding, or pain.

Results

Results should take about 30 minutes.

A normal range for HbA1c is 5.7%. Over 6.5% points to diabetes. A level between 5.7% and 6.4% points to prediabetes.

HbA1c is part of a diabetes management. The range differs from person to person. Your care team will adjust your care plan based on the results.

Higher than normal levels of HbA1c may be caused by:

  • Treatment with corticosteroids or other medicines
  • Higher than normal triglycerides
  • Iron-deficiency anemia
  • High bilirubin level
  • Kidney failure
  • Having your spleen removed
  • Cushing syndrome
  • Pheochromocytoma
  • Polycystic ovary syndrome

Lower than normal levels of HbA1c may be caused by:

  • Overdose of vitamin C or E
  • Pregnancy
  • Transfusion
  • Blood loss
  • Hemolytic anemia

Health conditions linked to hemoglobin problems can also affect results.

Your doctor will talk to you about the results. A test may point to an illness that you do not have. It can also miss an illness that you may have. The doctor will check your symptoms and all test results before making a diagnosis.

REFERENCES:

Glycemic control monitoring. EBSCO DynaMed website. Available at:http://www.dynamed.com/topics/dmp~AN~T114088/Glycemic-control-monitoring. Updated March 7, 2019. Accessed July 18, 2019.

HbA1c measurement. EBSCO DynaMed website. Available at:http://www.dynamed.com/topics/dmp~AN~T906936/Hemoglobin-A1c-measurement. Updated March 13, 2019. Accessed July 18, 2019.

Hemoglobin A1c. Lab Tests Online—American Association for Clinical Chemistry website. Available at: https://labtestsonline.org/tests/hemoglobin-a1c. Updated April 19, 2019. Accessed July 18, 2019.

Last reviewed June 2019 by EBSCO Medical Review Board Nicole S. Meregian, PA