Although the rate of HLA-B27 positivity in patients with ankylosing spondylitis can be over 90%, approximately 80% of B27-positive individuals do not develop ankylosing spondylitis, so HLA-B27 positivity does not necessarily mean that they have ankylosing spondylitis. About 10% of patients with ankylosing spondylitis are B27-negative. Therefore, HLA-B27-negative patients cannot be excluded from having ankylosing spondylitis as long as the clinical presentation and imaging meet the diagnostic criteria.