HLA-B27 antigen

HLA-B27 antigen

Definition:

A blood test to detects the presence of HLA-B27 on lymphocytes (see also Histocompatibility antigens test). In the past, this test was performed using serum that specifically reacts with HLA-B27 on the cells (known as serologic tissue typing). Newer methods are now available that use genetic testing to identify the type of HLA-B27 in a particular individual. The HLA-B27 gene is designated as HLA-B*2701, HLA-B*2702, etc.

Alternative Names:

Human leukocyte antigen B27

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 for the test:

Adults:
No special preparation is usually 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 experiences, 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:

infant test or procedure preparation (birth to 1 year)
toddler test or procedure preparation (1 to 3 years)
preschooler test or procedure preparation (3 to 6 years)
schoolage test or procedure preparation (6 to 12 years)
adolescent test or procedure preparation (12 to 18 years)

How the test will feel:

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.

Why the test is performed:

The human leukocyte antigens (HLA) antigens are glycoproteins present in the cell membranes of all nucleated cells, and in especially high concentrations in leukocytes. HLA antigens are the major histocompatibility antigens for tissue recognition. They are especially important in considering any type of tissue transplant, for example, kidney transplant or bone marrow transplant.

Many HLA antigens exist, but some are of special interest since they are more common in certain autoimmune diseases. For example, HLA-B27 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 Caucasian people without autoimmune disease.

Using the new genetic testing methods, not all HLA-B27 genes are associated with an increased risk of developing ankylosing spondylitis (e.g., HLA-B*2706 has not been shown to have an association). Importantly, this test does not predict the development of autoimmune disease, and should not be used for this purpose.

Normal Values:

HLA-B27 is found in 5 to 7% of Caucasian people without autoimmune disease.

What abnormal results mean:

A positive test indicates a greater than average risk for developing:

ankylosing spondylitis
Reiter's syndrome
sacroiliitis (inflammation of the sacroiliac joint)

In the presence of suggestive clinical findings, a positive HLA-B27 test may confirm the diagnosis.

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.

Review Date: 12/5/2001
Reviewed By: Michael C. Milone, M.D., Ph.D., Department of Pathology and Laboratory Medicine, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

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