HLA-B27 is a blood test to look for a protein that is found on the surface of white blood

cells. The protein is called human leukocyte antigen B27 (HLA-B27). Human leukocyte

antigens (HLAs) are proteins that help the body's immune system tell the difference between

its own cells and foreign, harmful substances.HLA B27 is also strongly associated with

diseases ankylosing spondylitis (AS), reactive arthritis (ReA), and other

spondyloarthropathies (SpA)