Alternative names
Human leukocyte antigen B27

Definition

This is a blood test to detect the presence of HLA-B27 on lymphocytes (white blood cells). 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.

How the test is performed

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to 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 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.

For an 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
No special preparation is usually necessary.

For infants and children:
The preparation you can provide for this test depends on your child’s age and previous experiences. For specific information regarding how you can prepare your child, see the following topics:

 
• 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 (HLAs) are proteins present on the surface of all body cells that contain a nucleus, and are in especially high concentrations in white blood cells (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 80-90% of people with ankylosing spondylitis and Reiter’s syndrome. However, HLA-B27 is also present in 5-7% 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 (for example, HLA-B*2706 has not been shown to have an association). It is important to note that 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.

Medical Encyclopedia

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.