HLA-B27 is a variant of a normal immune-system gene (human leukocyte antigen). It is much more common in people with ankylosing spondylitis, reactive arthritis, psoriatic arthritis and acute anterior uveitis, so the UK healthcare system uses a simple blood test as one piece of evidence when diagnosing spondyloarthritis. Being HLA-B27 positive does not mean you will develop disease — most carriers never do — and being negative does not rule it out. It is one clue among symptoms, examination and imaging.
What is hla-b27?
HLA-B27: HLA-B27 is a genetic marker present in ~90% of people with ankylosing spondylitis, but also in ~8% of the general UK population without disease. A positive test alone doesn't diagnose disease — clinical assessment and imaging are essential.
Last updated 2026-07-04. This is general information, not a substitute for personalised medical advice.