Hb electrophoresis; Hgb electrophoresis
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The area is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the elastic band to fill with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In an infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test
No special preparation is necessary for this test.
For infants and children:
The preparation you can provide for this procedure depends on your child’s age, previous experiences, and level of trust. For specific information on how you can prepare your child, see the following topics:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- Schoolage test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
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
This test is performed when a disorder associated with abnormal forms of hemoglobin (hemoglobinopathy) is suspected.
Although many different hemoglobin molecules have been described, the most common ones are HbA, HbA2, HbF, HbS, HbC, Hgb H, and Hgb M. In normal adults, only HbA and HbA2 are present at significant levels. Small amounts of HbF (which is the major Hb present in the fetus) may be present, but they are of no consequence unless levels are more than 2% of the total.
HbS is an abnormal form of hemoglobin associated with sickle cell anemia. HbS forms clumps in the presence of low oxygen, causing the red blood cells to take on a crescent or sickle shape. These misformed cells then 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 of various degrees of severity.
In adults, these hemoglobin molecules make up the total hemoglobin, as follows:
- Hgb A1: 95% to 98%
- Hgb A2: 2% to 3%
- Hgb F: 0.8% to 2%
- Hgb S: 0%
- Hgb C: 0%
In infants and children, these hemoglobin molecules make up the total hemoglobin, as follows:
- Hgb F (newborn): 50% to 80%
- Hgb F (6 months): 8%
- Hgb F (over 6 months): 1% to 2%
What abnormal results mean
The presence of significant levels of abnormal hemoglobins may indicate:
- Hemoglobin C disease
- Rare hemoglobinopathy
- Sickle cell anemia
Thalassemia is an additional condition under which the test may be performed.
What the risks are
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
A blood transfusion within the previous 12 weeks can produce falsely normal or abnormal results.
Veins and arteries vary in size from one patient to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
by Armen E. Martirosyan, M.D.