Definition of Histocompatibility antigen test:

A histocompatibility antigen blood test looks at proteins called human leukocyte antigens (HLAs), which are found on the surface of nearly every cell in the human body. HLAs are found in large amounts on the surface of white blood cells. They help the immune system tell the difference between body tissue and foreign substances.

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 site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

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, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area 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:

The results from this test can be used to identify good matches for tissue grafts and organ transplants, such as a kidney transplant or bone marrow transplant.

It may also be used to:

• Diagnose certain autoimmune disorders
• Determine relationships between children and parents when such relationships are in question (However, newer, more specific genetic testing is now available for this purpose)
• Monitor treatment with certain medications