Histocompatibility antigen test

Definition

A histocompatibility antigen blood test looks at inherited proteins on the surface of cells. The results from such a test can be used to match donated tissue to organ transplant recipients.

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 puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell 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 infants or young children:

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. A bandage may be applied to the puncture site if there is any bleeding.

How to prepare for the test

No preparation is necessary.

How the test will feel

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

HLA (human leukocyte antigens) are proteins found in the membranes (outer coating) of nearly every cell in the body (all cells that have a nucleus). These antigens are in especially high concentrations on the surface of white blood cells (leukocytes).

HLA antigens are the major determinants used by the body's immune system for recognition and differentiation of self from non-self (foreign substances). There are many different major histocompatibility (HLA) proteins, and each person possesses only a small, relatively unique set that is inherited from their parents. It is unlikely that 2 unrelated people will have the same HLA make-up.

Children, on average, will have one-half of their HLA antigens that match one-half of the mother's antigens. The other one-half of the child's antigens will match one-half of the father's antigens. This is particularly important in identifying good matches for tissue grafts and organ transplants, such as a kidney transplant or bone marrow transplant.

Many HLA molecules exist, but some are of special interest because they are more common in certain autoimmune diseases. For example, HLA-B27 antigen is found in 80-90% of people with ankylosing spondylitis and Reiter's syndrome, and can aid in the diagnosis of these diseases. HLA-B27 is also present in 5-7% of people without autoimmune disease. Thus, the mere presence of this HLA molecule is not indicative of disease.

HLA types can also used to determine relationships between children and parents when such relationships are in question. However, newer, more specific genetic testing is now available for this purpose.

Normal Values

Each person has unique HLA antigens, although identical twins may match each other.

What abnormal results mean

Each person has unique HLA patterns. However, some HLA types are associated with certain conditions (see "Why is the test performed").

What the risks are

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

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.

Illustrations

Blood test

Bone Tissue

Page Content:

HLA typing; Tissue typing ; hla typing; tissue typing