Jun 25, 2011
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 used as one piece of evidence in a constellation of signs, symptoms, and lab tests to support or rule out the diagnosis of certain autoimmune disorders, such as AS and reactive arthritis.
AS and reactive arthritis are both chronic, progressive conditions that occur more frequently in men than women. The first symptoms typically occur 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, eyes, and 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.
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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 an autoimmune disorder that is associated with the presence of HLA-B27. Doctors frequently must rely on their clinical findings and the HLA-B27 test result when diagnosing ankylosing spondylitis, and other HLA-B27-related disorders, because the characteristic changes to the bones may not be detectable for several years. Under these circumstances, HLA-B27 is not diagnostic but adds additional information, increasing or decreasing the likelihood that the patient has ankylosing spondylitis. An HLA-B27 may also be ordered when someone has recurrent uveitis.
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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 association is not there. This does not, however, mean that the person does not have the suspected condition, as a certain percentage of people with each disorder will be HLA-B27 negative.
Ankylosing spondylitis: about 90% are HLA-B27 positive
Juvenile rheumatoid arthritis (JRA): about 80% are HLA-B27 positive
Reactive arthritis: about 60-85% are HLA-B27 positive
Isolated acute anterior uveitis: about 40-70% are HLA-B27 positive
Whether or not HLA antigens will be present is genetically determined. Their production is controlled by genes that are passed from parents to children. If a person has a close family member with an HLA-B27 related disease that affects the joints of the spine (AS or other related condition) and is positive for the HLA-B27 antigen, then that person is at an increased risk of developing a similar disease.
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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, about fifteen different subtypes have been identified. The most common in the U.S. are 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.
HLA B27 (Human Leukocyte Antigen B27) is associated with a certain set of autoimmune diseases including psoriatic arthritis.
A blood test is often carried to establish a diagnosis particularly in ankylosing spondylitis.
In ankylosing spondylitis (AS). 90% of patients will have a positive test for HLA B27.
In psoriatic arthritis (PsA) 20% of patients will have a positive test for HLA B27.
50% of HLA B27 positive tests will have spinal disease (spondylopathy)
7% percent of the general population have the HLA-B27 gene