HLA-B27 is associated with Ankylosing Spondylitis but its presence...

• A. Always positive in AS
• B. Sometimes positive but not required for diagnosis
• C. Never positive in AS
• D. Only in psoriatic arthritis

Answer: (B)

HLA-B27 is a genetic marker that increases the risk of developing Ankylosing Spondylitis, but it is not needed to make the diagnosis. In many people with AS, this marker is present, yet a meaningful number of AS patients are HLA-B27 negative, and a substantial portion of healthy individuals carry HLA-B27 without ever developing AS. Because of this imperfect specificity, the presence of HLA-B27 supports the diagnosis when clinical symptoms and imaging fit, but it is not required and cannot by itself confirm or exclude the disease. The marker is also seen in related spondyloarthropathies, so it’s helpful for risk stratification and context, not a standalone diagnostic test. That’s why the best statement is that HLA-B27 can be positive, but it’s not mandatory for diagnosis.