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HLA-B27


At a Glance

Why Get Tested?

To determine whether you have human leukocyte antigen B27 (HLA-B27) on the surface of your cells; to help assess the likelihood that you have an autoimmune disorder associated with the presence of HLA-B27

When to Get Tested?

When you have symptoms of arthritis-like chronic joint pain, stiffness, and inflammation in certain areas of your body, such as your lower back, hips, neck, and chest, or have painful inflammation of the eyes called uveitis, especially if you are male and the symptoms began in your early 30s

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

HLA-B27 is a specific protein (termed a human leukocyte antigen or HLA) that is found on cell surfaces. The term HLA-B27 is also used to refer to the gene that codes for the HLA-B27 protein. The HLA-B27 test determines the presence or absence of HLA-B27 protein on the surface of a person's white blood cells.

Human leukocyte antigens are proteins that help the body's immune system identify its own cells and distinguish between "self" and "nonself." Everyone has an inherited combination of HLA genes that code for the many antigens present on the surfaces of their cells. The presence or absence of each antigen creates a distinctive HLA combination for each person.

HLA-B27 is found in about 6% of the U.S. population. People with HLA-B27 have an increased likelihood of developing autoimmune diseases such as ankylosing spondylitis (AS), juvenile rheumatoid arthritis (JRA),reactive arthritis (of which one subset is Reiter syndrome), and isolated acute anterior uveitis. HLA-B27 has also been linked with inflammatory bowel disease and a range of other chronic conditions.

While HLA-B27 has not been established as a cause of any of these disorders, there is a higher prevalence of the antigen in those affected.For example, even though only 6% of the population has HLA-B27, approximately 88% of people with ankylosing spondylitis are positive for HLA-B27.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

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 a definitive test that can be used to diagnose or rule out a disorder.It 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.

Ankylosing spondylitis and reactive arthritis are both chronic, progressive conditions that occur more frequently in men than women. The first symptoms typicallyoccur when a person is in their early 30's. Often, the initial symptoms of these autoimmune disorders are subtle and may take several years before characteristic degenerative changes to bones and joints are visible on X-rays.

  • Ankylosing spondylitis is characterized by pain, inflammation, and a gradual stiffening of the spine, neck and chest.
  • Reactive arthritis is a group of symptoms that includes inflammation of the joints, urethra, and eyes as well as skin lesions.
  • Juvenile rheumatoid arthritis is a form of arthritis that occurs in children.
  • Anterior uveitis is associated with recurring inflammation of the structures of one or both eyes.

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

When is it ordered?

An HLA-B27 test may be ordered when a person has acute or chronic pain and inflammation in the spine, neck, chest, eyes, and/or joints, and the doctor suspects the cause is an autoimmune disorder that is associated with the presence of HLA-B27. An HLA-B27 may also be ordered when someone has recurrent uveitis.

The HLA-B27 test is not diagnostic, but the results add information, increasing or decreasing the likelihood that the person being evaluated has the suspected autoimmune disorder.

Doctors frequently use the HLA-B27 test result when they suspect ankylosing spondylitis but the disease is in an early stage and the vertebrae in the spine have not yet undergone the characteristic changes that would be seen on X-ray.

What does the test result mean?

If a person is positive for HLA-B27 and has symptoms such as chronic pain, inflammation, and/ or degenerative changes to his bones (as seen on X-ray), then it supports a diagnosis of ankylosing spondylitis, reactive arthritis, or another autoimmune disorder that is associated with the presence of HLA-B27. This is especially true if the person is young, male, and if he experienced his first symptoms before the age of 40.

If HLA-B27 is negative, then the marker was not detected. This does not mean, however, that the person tested does not have the suspected condition since people who do not have the HLA-B27 antigen can also develop these autoimmune diseases. Likewise, someone who has the HLA-B27 antigen will not necessarily develop one of these conditions. Researchers are trying to determine what factors contribute to the higher likelihood of people with HLA-B27 developing these particular diseases and what actually triggers them.

Whether or not certain HLA antigens will be present is genetically determined. Their production is controlled by genes that are passed from parents to their children. 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.

Is there anything else I should know?

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, more than 70 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.



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