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.
Human leukocyte antigen B27
How the Test is Performed
A blood sample is needed. Most of the time blood is drawn from a vein located on the inside of the elbow or the back of the hand.
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 to help determine the cause of joint pain, stiffness, or swelling. The test may be done along with other tests, including:
A normal (negative) result means HLA-B27 is absent.
What Abnormal Results Mean
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 or ulcerative colitis
- Psoriatic arthritis (arthritis associated with psoriasis)
- Reactive arthritis or Reiter's syndrome
- Sacroiliitis (inflammation of the sacroiliac joint)
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)
Inman RD. The spondyloarthropathies. In: Goldman L, Schafer AI, eds.Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 273.