Test Details: The presence of HLA-B27 on white blood cells can cause immune system to attack those otherwise healthy cells. When this occurs, it can result in an autoimmune disease or immune-mediated disease such as juvenile rheumatoid arthritis or ankylosing spondylitis. With lower frequency, the presence of the HLA-B27 allele can be correlated with inflammatory bowel disease, psoriatic arthritis and reactive arthritis.