HLA-B27
HLA-B27 is a type of human leukocyte antigen (HLA), which is part of a larger complex protein molecule (MHC I). It plays an important role in the functioning of the immune system: it is a cell-surface molecule on the surface of white blood cells, which is responsible for recognizing and distinguishing the body’s own proteins from foreign protein, such as bacteria and viruses.
What does the test show?
The assay can be used to determine the presence of the HLA-B27 gene. This gene predisposes to the development of certain joint autoimmune diseases.
Many joint diseases are caused by a malfunction of the immune system. In such cases, the immune system identifies each cell in the joints as infected and attacks them in response. Immune cells, when they get into the joint cells, cause permanent inflammation.
HLA-B27, a specific protein that can be detected on the surface of white blood cells, helps identify foreign substances for the immune system.
Everyone has a unique combination of human leukocyte antigens (HLA), but the HLA-B27 gene is present in only 5-8% of the population. However, the presence of the gene does not indicate a clear predisposition to autoimmune disease, with only 2% of carriers suffering from any of the diseases it affects.
Autoimmune diseases affected by the presence of the HLA-B27 gene include Bechterew’s disease (ankylosing spondylitis, or AS), reactive arthritis (Reiter’s syndrome), arthritis associated with inflammatory bowel disease, and uveitis.
In which cases is it recommended to perform the test?
Determination of HLA-B27 antigen from a blood sample is required in case of suspicion of certain joint autoimmune diseases (Bechterew’s disease, Reiter’s syndrome, juvenile arthritis, arthritis associated with inflammatory bowel disease, uveitis). However, the test is not specific and clearly does not diagnose any disease. The diagnosis can only be made with an accurate knowledge of the symptoms and with other laboratory tests.
It is usually prescribed at the same time as other tests for chronic arthritis, joint pain, the presence of joint stiffness, and suspected autoimmune disease.
What sample is needed for the test?
A blood sample taken from a vein is needed to perform the test.
What can the result indicate?
The test result determines the presence of the HLA-B27 gene, however, there is no clear diagnosis of any of the affected autoimmune diseases.
HLA-B27 positivity refers to the presence of the gene, which indicates an increased dispositon to the following autoimmune diseases: Bechterew’s disease, Reiter’s syndrome, juvenile arthritis, arthritis associated with inflammatory bowel disease, and uveitis. However, the presence of the gene does not necessarily mean the development of these diseases, with only 2% of carriers suffering from any of these diseases.
If the test is negative, the gene is not found in the body. However, this does not mean that the autoimmune diseases mentioned above do not develop in the individual, as patients do not always carry the gene.
What to do after the test?
In all cases, consult the rheumatologist who ordered the test with the results, as the finding is not of diagnostic value in itself. The diagnosis can only be made in the knowledge of the symptoms, and at the same time as other laboratory and imaging diagnostic tests.
