A blood sample is needed. For information on how this is done, see: Venipuncture
How to prepare for the test
No special preparation is necessary for this test.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
You may have this test if your health care provider suspects that you have a disorder caused by abnormal forms of hemoglobin (hemoglobinopathy).
Many different types of hemoglobin (Hb) exist. The most common ones are HbA, HbA2, HbF, HbS, HbC, Hb H, and Hb M. Healthy adults only have significant levels of HbA and HbA2.
Some people may also have small amounts of HbF (which is the main type of hemoglobin in an unborn baby's body). Certain diseases are associated with high HbF levels (when HbF is more than 2% of the total hemoglobin).
HbS is an abnormal form of hemoglobin associated with sickle cell anemia. In people with this condition, the red blood cells sometimes have a crescent or sickle shape. The cells easily break down, or can block small blood vessels.
HbC is an abnormal form of hemoglobin associated with hemolytic anemia. The symptoms are much milder than they are in sickle cell anemia.
Other, less common, abnormal Hb molecules cause anemias.
In adults, these hemoglobin molecules make up the following percentages of total hemoglobin:
Hb A: 95% to 98%
Hb A2: 2% to 3%
Hb F: 0.8% to 2%
Hb S: 0%
Hb C: 0%
In infants and children, these hemoglobin molecules make up the following percentages of total hemoglobin:
Hb F (newborn): 50% to 80%
Hb F (6 months): 8%
Hb F (over 6 months): 1% to 2%
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What abnormal results mean
The presence of significant levels of abnormal hemoglobins may indicate:
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
You may have false normal or abnormal results if you've had a blood transfusion within the previous 12 weeks.
Todd Gersten, MD, Hematology/Oncology, Palm Beach Cancer Institute, West Palm Beach, FL. Review provided by VeriMed Healthcare Network. Also reviewed by Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington; David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.