A histocompatibility antigen blood test is also known as “HLA” testing, a state of mutual tolerance that allows some tissues to be grafted effectively to others 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. Most HLA laboratories utilize molecular methodologies for typing patients at several HLA loci and a variety of test methodologies for HLA antibody screening and crossmatching.
Human leukocyte antigens (HLA) are genes in major histocompatibility complexes (MHC) that help code for proteins that differentiate between self and non-self. They play a significant role in disease and immune defense. They are beneficial to the immune system but can also have detrimental effects.
HLA types also had correlations with an increased risk of particular diseases. For example, early-onset myasthenia gravis correlates with HLA-B8 as the unique genetic factor that leads to the onset of the disease.[rx] Although of unknown etiology, multiple sclerosis has been shown to have a high rate of correlation with the HLA-DR2 antigen.[rx] Additionally, rheumatoid arthritis (RA) has been shown to precipitate complex biological interactions in the body. Some of these interactions include HLA-DR4, a glycopeptide from type II collagen, and a T-cell receptor, shown to be correlated with the development of RA.[rx]
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
HLA testing involves either a blood sample or a cheek swab. The sample is then sent to a laboratory that assesses groups of related HLA genes that form the major histocompatibility complex. HLA testing also analyzes HLA antibodies. The test determines if someone is a good match for someone needing a transplant.
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 transplants.
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 and half of their HLAs match half of their fathers.
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, the 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
