The HLA-B27 test detects the presence of the HLA-B27 antigen in a sample using PCR (Polymerase Chain Reaction). This test is primarily used to support or confirm the diagnosis of conditions such as ankylosing spondylitis (AS), Reiter’s syndrome (reactive arthritis), and sometimes anterior uveitis. A positive result can indicate a higher risk for these autoimmune and inflammatory disorders, although it is not definitive on its own, as not everyone with the HLA-B27 antigen will develop these conditions.