HLA typing; Tissue typing
A histocompatibility antigen blood test looks at proteins called human leukocyte antigens (HLAs). These are found on the surface of almost all cells 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 substances that are not from your own body.
How the Test is Performed
Blood is drawn from a vein. In most cases a vein on the inside of the elbow or the back of the hand is used. First, the site where blood will be drawn is cleaned with germ-killing medicine (antiseptic). Then, 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 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
You do not need to prepare for this test.
How the Test Will Feel
You may feel slight pain or a sting when the needle is inserted. 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. These may include kidney transplants 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
- Monitor treatment with some medicines
Normal Results
You have a small set of HLAs that are passed down from your parents. Children, on average, will have half of their HLAs match half of their mother’s and half of their HLAs match half of their father’s.
It is unlikely that two unrelated people will have the same HLA makeup. However, identical twins may match each other.
Some HLA types are more common in certain autoimmune diseases . For example, HLA-B27 antigen is found in many people (but not all) with ankylosing spondylitis and Reiter syndrome .
Risks
Slight risks from having blood drawn may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Bruising
