Also known as: HLA-B27 antigen
Name: Human leucocyte antigen B27
Related tests: C-reactive protein , ESR, Rheumatoid factor
Why get tested?
To determine whether the HLA-B27 antigen is present on the surface of white blood cells, which helps diagnose certain autoimmune diseases.
When to get tested?
When there are symptoms associated with chronic inflammation, such as pain and stiffness in parts of the body such as the back, knees and elbows, especially if the patient is male and the symptoms appear before the age of thirty.
What sample is required?
A blood sample from a vein
What is being tested?
The test determines whether the human B27 antigen is present on the surface of white blood cells in a blood sample taken from a vein. Human leucocyte antigens (HLA) are a group of proteins that help the immune system tell the body’s “own” cells from foreign ones; they therefore distinguish “self” from “non-self”. Each person has their own combination of HLA antigens on the surface of their white blood cells and other nucleated cells. HLA antigens are divided into different types: class 1 (A, B, C) and class 2 (DR, DP, DQ). Although none of these is specific to one person, the presence or absence of each antigen creates a combination that is unique to each individual.
The B27 antigen has been found in approximately 5-10% of the US population. Its presence is associated with autoimmune diseases. The most common disease associated with this antigen is ankylosing spondylitis: about 90% of patients with this disease test positive. Other diseases linked to B27 are:
• Juvenile rheumatoid arthritis, with 80% of affected patients positive for the antigen.
• Reiter’s syndrome (also known as reactive arthritis), with 50-80% of patients positive for HLA-B27.
• Acute anterior uveitis, with about 40-70% of cases positive.
HLA-B27 is also found in patients with inflammatory bowel disease and other chronic diseases.
While HLA-B27 has not been shown to cause these diseases, it is highly prevalent in them.
How is the sample collected?
A blood sample is taken from a vein in the arm.
Is any preparation needed for the test?
No.
How is it used?
When is the test requested?
How should the test result be interpreted?
Is there anything else I should know?
How is it used?
The test is often requested to confirm a diagnosis of ankylosing spondylitis, Reiter’s syndrome and sometimes anterior uveitis. It cannot be used as a diagnostic test on its own, but it provides an additional piece of information within an overall picture of symptoms and other laboratory tests.
Both ankylosing spondylitis and Reiter’s syndrome are chronic, progressive diseases; they are more common in men than in women, and the first symptoms usually appear before the age of thirty.
Ankylosing spondylitis is characterised by pain, inflammation and progressive stiffening of the spine, neck and chest.
Reiter’s syndrome is characterised by other symptoms, such as inflammation of the joints, urethra and eyes, and skin lesions.
In autoimmune diseases the first symptoms are often very mild, and it takes many years before bone degeneration can be seen on X-rays.
Anterior uveitis is associated with recurrent inflammation of one or both eyes.
The HLA-B27 test is often combined with other tests to give a more complete diagnostic picture.
These tests are rheumatoid factor, ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein).
HLA-B27 is often used in cases of recurrent uveitis with no recognisable cause.
When is the test requested?
When the doctor suspects that the patient has an autoimmune disease because of acute or chronic pain and inflammation affecting the spine, knee or rib cage.
This test is particularly useful in diagnosing ankylosing spondylitis and other diseases, because bone lesions cannot be seen on X-rays in the first years of the disease
The test is also requested for patients with recurrent uveitis.
How should the test result be interpreted?
The antigen is either present or absent on the surface of white blood cells and other nucleated cells, so the result is positive or negative. If a patient who tests positive has symptoms such as chronic pain, inflammation and bone degeneration, they very probably have an autoimmune disease. This is particularly likely if the patient is young and male and the symptoms appeared before the age of forty.
A negative test does not completely rule out autoimmune disease; in a small percentage of cases these diseases are present without this antigen.
The presence of the antigen in people without any symptoms is not clinically significant
Is there anything else I should know?
Whether a person has the HLA-B27 antigen is genetically determined. If there are cases of autoimmune diseases associated with HLA-B27 in a patient’s family and the patient also has the antigen on their cells, they have a high chance of developing the disease.
Thanks to molecular biology it is now possible to identify different subtypes of HLA-B27. About 15 different subtypes have been identified; in the United States the most common are HLA-B27*05 and HLA-B27*02. It is not yet clear whether the antigen subtype is linked to disease progression
1. What causes autoimmune diseases?
1. What causes autoimmune diseases?
In many cases this is not yet clear; in some cases of Reiter’s syndrome an association has been seen with a previous infection with microorganisms such as Chlamydia, Campylobacter, Salmonella or Yersinia. There is in fact a similarity between the antigens on the surface of these microorganisms and the HLA-B27 antigen on the patient’s tissue cells, against which the immune system is activated after the infection has resolved.