HLA-B27 (Human Leukocyte Antigen B27)

Other names for HLA-B27 (Human Leukocyte Antigen B27):

Human lymphocyte antigen B27, human leukocyte A antigen, histocompatibility leukocyte A antigen

The HLA-B27 test is primarily ordered to help strengthen or confirm a suspected diagnosis of ankylosing spondylitis (AS), reactive arthritis, juvenile rheumatoid arthritis (JRA), or sometimes anterior uveitis. The HLA-B27 test is not diagnostic; that is, it is not a definitive test that can be used to diagnose or rule out a disorder. The result adds information and is one piece of evidence used along with the evaluation of signs, symptoms, and other laboratory tests to support or rule out the diagnosis of certain autoimmune disorders, such as ankylosing spondylitis and reactive arthritis.

The HLA-B27 test may be ordered as part of a group of tests used to help diagnose and evaluate conditions causing arthritis-like chronic joint pain, stiffness, and inflammation. This group of tests may include a rheumatoid factor (RF) with either an erythrocyte sedimentation rate (ESR) or a C-reactive protein (CRP). HLA-B27 is sometimes ordered to help evaluate someone with recurrent uveitis that is not caused by a recognizable disease process.

Causes:

In most cases, the cause is not known. However, in some cases of reactive arthritis, there is an association between a previous infection by a microbe, such as Chlamydia, Campylobacter, Salmonella, Ureaplasma, or Yersinia, and the onset of the disease. It is thought that similarities between the HLA-B27 antigen and the antigens found on the surface of the microbes trigger the immune system to fight both the microbe and the person’s own tissues, launching the autoimmune disorder after the resolution of the infection.

Genetics:

Whether or not certain HLA antigens will be present is genetically determined. Genes that are passed from parents to their children control the production of those antigens. If two members of the same family are HLA-B27 positive and one of them develops a disease associated with HLA-B27, then the other person is at an increased risk of developing a similar disease.

Though the diseases associated with HLA-B27 occur more frequently in men, women can also be affected. However, the signs and symptoms related to the diseases can often be milder in women.

With new genetic testing methods, it is now possible to separate HLA-B27 into subtypes. So far, at least 105 different subtypes have been identified, such as HLA B27*05 and HLA B27*02. How the presence of these specific subtypes affects the likelihood of developing an autoimmune disease is not yet known.

Other tests:

If your HLA-B27 antigen test is positive, you may need other tests to help confirm a diagnosis of an autoimmune disease. You may have tests such as:

- Erythrocyte sedimentation rate (ESR) which may show you have inflammation

- C-reactive protein, which also can look for inflammation

- Joint X-rays or MRI

- Urine test

Your results:

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

A negative result means you don't have HLA-B27 in your blood. A positive result means HLA-B27 was found in your blood. You may have a higher-than-average risk of certain autoimmune diseases, such as ankylosing spondylitis and reactive arthritis. If you are white, you are more likely to test positive for the HLA-B27 antigens.