Hemoglobin electrophoresis
Alternative names:
Hb electrophoresis; Hgb electrophoresis
How the test is performed:
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (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 tourniquet 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.
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:
Adults:
No special preparation is necessary for this test.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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 Hb 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 associated with sickle cell anemia. HbS, in the presence of low O2 concentrations, precipitates. The precipitated HbS causes the red blood cells to sickle (form a crescent shape), which results in a blockage of small vessels and breakdown (lysis) of some of the cells.
HbC is an abnormal hemoglobin form associated with a hemolytic anemia, because the red blood cells are more fragile than normal. The symptoms are much more mild than they are in sickle cell anemia.
Other, less common, abnormal Hb molecules cause anemias of various degrees of severity.
|
