HLA-B27

With genetic testing it is possible to classify HLA-B27 alleles into different subtypes. To date, more than 160 different subtypes have been described.

It is not yet known how the individual subtypes affect the likelihood of developing an autoimmune disease.

This test is usually performed in people presenting with acute or chronic pain and inflammation in the back, neck, chest, eyes or joints, when there is suspicion of an autoimmune disease associated with the presence of the HLA-B27 allele. It is also sometimes requested to evaluate cases of recurrent uveitis.

HLA-B27 testing is primarily used to confirm a suspected diagnosis of ankylosing spondylitis, juvenile rheumatoid arthritis, reactive arthritis and some cases of anterior uveitis.

It should be made clear that the HLA-B27 test is not diagnostic for any disease and cannot be used to diagnose or rule out disease. It should be used and evaluated in conjunction with the patient’s signs and symptoms and other laboratory tests to diagnose or rule out a range of autoimmune diseases.

As mentioned above, this is not a diagnostic test. Evaluation of the symptoms and the results of other tests are necessary to be able to determine the possible disease. 

That is, if the test result is positive and the person has symptoms such as chronic joint pain, inflammation or degenerative bone changes (visible on X-rays), it is very likely that he/she has an autoimmune disease associated with HLA-B27 (ankylosing spondylitis, Reiter’s syndrome, reactive arthritis…) The probability is higher if it is a young man who starts to have symptoms before the age of 40.

However, being HLA-B27 positive does not imply that you will develop these diseases. 

If the result is negative, it means that the marker is not in the cell. However, the presence of the disease cannot be ruled out, as some people can develop autoimmune diseases even if they do not have the HLA-B27 allele. 

Most of the time the cause is not known. However, in some reactive arthritis there is an association between the development of the disease and a previous infection with microorganisms such as Chlamydia, Campylobacter, Salmonella, Ureaplasma or Yersinia. It is thought that the similarities between HLA-B27 and the antigens present on the surface of these micro-organisms may trigger the immune system to attack both the micro-organism and its own tissues, leading to autoimmune disease once the infection has resolved.

It is an inflammatory disease that mainly affects the joints of the spine, which tend to weld together, decreasing their flexibility and producing a stiffness of the spine. It is one of a group of rheumatic diseases called spondyloarthropathies.

The cause of the disease is unknown, although genes appear to play a role. Most people with ankylosing spondylitis (about 90%) are positive for the HLA-B27 allele.

Reiter’s syndrome, also known as reactive arthritis, is a condition ranging from an inflammatory reaction to an infection somewhere in the body. It usually follows an infection of the urinary tract, genital tract or digestive tract.
The following parts of the body may be affected:

• Eyes causing conjunctivitis and/or uveitis
• Joints leading to reactive arthritis
• Urethr
• Skin 

Although the exact origin of this disease is unclear, apart from urinary tract infections and intestinal infections caused by food poisoning, the presence of the HLA-B27 allele has also been associated with this disease.