HLA B27 (human leukocyte antigen) is a protein found on the surface of white blood cells of certain individuals. The presence of antigens on the surface of cells allows the immune system to distinguish its own cells from foreign cells. The presence of HLA B27 (8% of the population) is associated with a higher risk of developing certain autoimmune diseases such as ankylosing spondylitis, reactive arthritis, isolated eye disorders (uveitis), etc. The test is useful for individuals suffering from acute or chronic inflammation and pain in the spine, neck, chest, eyes and joints that is suspected to be caused by an autoimmune disorder.
A positive HLA B27 indicates that the individual is at higher risk of developing an autoimmune disease. In the presence of the appropriate symptoms, a positive HLA B27 can support a diagnosis of ankylosing spondylitis, reactive arthritis or other. A negative HLA B27 does not, however, completely rule out the possibility of developing one of the autoimmune disorders mentioned above. The presence or absence of the different HLAs is genetically determined. If two members of the same family are positive for HLA B27 and one of them has developed one of the associated diseases, it is very likely that the other person will also develop a similar disease.