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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.
Ankylosing spondylitis 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, 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.
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, 80-90% 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.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.