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

Human leukocyte antigen B27

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

No special preparation is usually needed.

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.

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.

A normal (negative) result means HLA-B27 is absent.

A positive test means HLA-B27 is present. It suggests a greater-than-average risk for developing or having certain autoimmune disorders. An autoimmune disorder is a condition that occurs when the immune system mistakenly attacks and destroys healthy body tissue.

An abnormal result may be caused by:

• Ankylosing spondylitis
• Arthritis related to Crohn's disease
• Reactive arthritis
• Sacroiliitis (inflammation of the sacroiliac joint)
• Uveitis

If there are symptoms or signs of an autoimmune disease, a positive HLA-B27 test may confirm the diagnosis. However, HLA-B27 is normally found in a small number of Caucasians and does not always mean you have a disease.

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.

Other risks associated with having blood drawn are slight but 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)

Miller FW. The spondyloarthropathies. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 286.

van der Linden SM, van der Heijde D, Maksymowych WP. Ankylosing spondylitis. In: Firestein GS, Budd RC, Harris ED, et al, eds. Kelley’s Textbook of Rheumatology. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2009:chap 70.