A gene called HLA-B27 is found in more than 90% of people with ankylosing spondylitis. Thus, it is possible to have ankylosing spondylitis without having the gene, but unlikely.
However, having a positive test for the HLA-B27 gene does not mean that ankylosing spondylitis is present or that it will develop. A healthy person who carries the HLA-B27 gene and has no relatives with ankylosing spondylitis has only a 2% chance of getting this form of arthritis.
If ankylosing spondylitis is suspected, a blood test to identify if the HLA-B27 gene is a standard part of the diagnostic process .