HLA-B27 antigen

Definition

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. They are made from instructions by inherited genes.

Alternative Names

Human leukocyte antigen B27; Ankylosing spondylitis-HLA; Psoriatic arthritis-HLA; Reactive arthritis-HLA

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 steps are needed to prepare for the test.

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 health care provider 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:

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

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

Normal Results

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.

A positive result can help your provider make a diagnosis of a form of arthritis called spondyloarthritis. This kind of arthritis includes the following disorders:

• Ankylosing spondylitis
• Arthritis related to Crohn disease or ulcerative colitis
• Psoriatic arthritis (arthritis associated with psoriasis)
• Reactive arthritis
• Sacroiliitis (inflammation of the sacroiliac joint)
• Uveitis

If you have symptoms or signs of spondyloarthritis, a positive HLA-B27 test may help confirm the diagnosis. However, HLA-B27 is found in some normal people and does not always mean you have a disease.

Risks

Risks from having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

References

Bray R, Sullivan HC, Krummey S, Gebel HM. Human leukocyte antigen: the major histocompatibility complex of humans. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 50.

Chernecky CC, Berger BJ. Human Leukocyte Antigen (HLA) B-27 - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:654-655.

Lienesch DW. Spondyloarthritis. In: Wing EJ, Schiffman FJ, eds. Cecil Essentials of Medicine. 10th ed. Philadelphia, PA: Elsevier; 2022:chap 80.

McPherson RA, Massey HD. Overview of the immune system and immunologic disorders. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 44.

Reveille JD. Spondyloarthritis. In: Rich RR, Fleisher TA, Shearer WT, Schroeder HW, Frew AJ, Weyand CM, eds. Clinical Immunology: Principles and Practice. 5th ed. Philadelphia, PA: Elsevier; 2019:chap 57.