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Histocompatibility antigens 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:
Adults:
No preparation is necessary.
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 it Feels:
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 .
Risks:
- 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
Why this Test is Performed:
HLA (human leukocyte antigens) antigens are glycoproteins present in the cell membranes of nearly every cell in the body (all nucleated cells). These antigens are in especially high concentrations on the surface of white blood cells (leukocytes).
HLA antigens are the major histocompatibility antigens for tissue recognition. There are many specific HLA antigens. It is unlikely that 2 unrelated people will have the same HLA makeup. Children, on the average, will have one-half of their HLA antigens that match one-half of their mothers antigens; the other one-half of the child's antigens will match one-half of their father's antigens. This is particularly important in determining the "match" for tissue grafts and organ transplants, such as a kidney transplant or bone marrow transplant .
Many HLA antigens exist, but some are of special interest because they are more common in certain autoimmune diseases . For example, the HLA-B27 antigen is found in 80 to 90% of people with ankylosing spondylitis and Reiter's syndrome . However, HLA-B27 is also present in 5 to 7% of people without autoimmune disease. HLA antigens are also measured to determine relationships between children and parents when such relationships are in question.
Normal Values:
Each person has unique HLA antigens (identical twins may match each other).
Abnormal Results:
Each person has unique HLA antigen patterns. However, some HLA antigens are associated with certain conditions (see "Why is the test performed").
Cost:
The estimated cost is $167.
Special Considerations:
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.
A photomicrograph of bone tissue. Bone tissue is obtained from a bone biopsy and examined under a microscope. This is a picture of how normal tissue appears when magnified.
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