For patients with low back pain and stiffness, doctors often recommend testing for HLA-B27. what exactly is HLA-B27 and what does being positive for HLA-B27 mean? HLA-B27 is a human gene expression product that is closely related to the development of spondyloarthropathies. The rate of HLA-B27 positivity in normal individuals is 6 to 8 percent. In ankylosing spondylitis, the HLA-B27 positivity rate is over 90%, and in patients with concurrent ocular uveitis, the positivity rate is 100%. In reactive arthritis, the HLA-B27 positivity rate is 60% to 80% when accompanied by sacroiliac arthritis or oculocutaneous uveitis. In patients with juvenile spondyloarthropathies, the positivity rate is 80%. In patients with psoriatic arthritis with spondylitis, the positivity rate was 50%. It is clear that HLA-B27 is closely related to spondyloarthropathies, but it does not necessarily mean that HLA-B27 positivity is a spondyloarthropathy, as there are some normal people who show positivity. HLA-B27-positive patients with ankylosing spondylitis have the following characteristics: 1. HLA-B27-positive patients have an earlier age of onset; 2. Acute iritis is more common in HLA-B27-positive patients; 3. Family aggregation is more pronounced in HLA-B27-positive patients; 4. Spinal involvement is more common in HLA-B27-positive patients; 5. HLA-B27-positive patients are more likely to have hip pain and hip HLA-B27 positive individuals are more likely to have hip pain and hip lesions; 6. HLA-B27 positive individuals have more severe inflammatory changes.