HLA-B27, also known as human leukocyte antigen B27, is the expression product of a gene. Some people inherit this gene from their parents and therefore test positive for HLA-B27, while those who do not inherit this gene may test negative. The expression of the HLA-B27 gene is closely related to ankylosing spondylitis, and people who are positive for HLA-B27 are more likely to develop ankylosing spondylitis than those who are negative. 90% of people with ankylosing spondylitis are positive for HLA-B27. There are many subtypes of HLA-B27, but the main ones that are closely associated with ankylosing spondylitis are HLA-B2704 and HLA-B2705. There may be some genetic differences between healthy people with HLA-B27 and those with ankylosing spondylitis, but the clinical diagnosis of ankylosing spondylitis does not rely exclusively on HLA-B27. The pathogenesis of ankylosing spondylitis is not clear, and is often associated with abnormal immune function and a genetic predisposition. The diagnosis of ankylosing spondylitis relies on the patient’s clinical symptoms and imaging. Therefore, if a patient presents with symptoms such as back pain and fatigue, he or she should immediately visit the rheumatology department of the hospital to clarify the cause through physical examination, erythrocyte sedimentation rate, and other relevant indicators.