Definition of HLA-B27 antigen:

HLA-B27 is a blood test to look for a protein that is found on the surface of white blood cells. The protein is called human leukocyte antigen B27 (HLA-B27).

Human leukocyte antigens (HLAs) are proteins that help the body's immune system tell the difference between its own cells and foreign, harmful substances.

See also: Histocompatibility antigen test

How the test is performed:

A blood sample is needed. For information on how this is done, see: Venipuncture

How to prepare for the test:

No special preparation is usually needed.

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:

Your doctor may order this test if you have joint pain, stiffness, or swelling. HLA type B27 is associated with autoimmune diseases such as ankylosing spondylitis and Reiter syndrome. The test may be done along with other tests, including:

• C-reactive protein
• Erythrocyte sedimentation rate ( ESR)
• Rheumatoid factor
• X-rays

HLA antigen testing is also used to match donated tissue in a person who is getting an organ transplant. For example, it may be done when a person needs a kidney transplant or bone marrow transplant.