B-27, known as HLA-B27, is a large class of HLA family protein molecules distributed in histocompatibility complexes on the surface of cells, which are responsible for mutual recognition between cells and induction of immune responses in the immune system, regulating the function of the immune response. Numerous studies have shown a strong correlation between B-27 and ankylosing spondylitis. When patients visit the rheumatology department due to back pain, doctors usually recommend B-27 testing, and it has been found that the positive rate of B-27 in patients with ankylosing spondylitis is over 90%, while the positive rate in the normal population is only 5-10%. Ankylosing spondylitis has many similarities in symptoms to other diseases, making it difficult to confirm the diagnosis; therefore, the B-27 test has great value in confirming the diagnosis of ankylosing spondylitis. Typically, the laboratory uses flow cytometry to detect B-27 expression results with 100% sensitivity and 99.99% negative results in patients with excluded ankylosing spondylitis. When a positive result is present prompt hospitalization should be done to avoid further progression of the disease, with hot compresses and physical therapy measures to massage the lumbar region. Combine treatment with tretinoin, nonsteroidal anti-inflammatory drugs, and biologic agents to avoid complications. (The specific drugs mentioned in the text should be prescribed according to the specialist’s interview).