What is being tested?This test detects the presence or absence of
human leukocyte antigen B27 (HLA-B27) on the surface of white blood cells in a blood sample. Human leukocyte antigens (HLA) are a group of
proteins that help the body’s immune system to identify its own cells and to distinguish between “self” and “nonself.” Everyone has an inherited combination of HLA antigens present on the surface of his or her white blood cells (leukocytes) and other nucleated (containing a
nucleus) cells. These HLA antigens are divided into types: Class I (A, B, C) and Class II (DR, DP, DQ). While not as unique as a fingerprint, the presence or absence of each
antigen creates a distinctive HLA combination for each person.
HLA-B27 is found in about 5-10% of the U.S. population. Its presence has been associated with several autoimmune disorders. The most common of these disorders is ankylosing spondylitis (AS). Approximately 90% of patients with AS are positive for HLA-B27. Other disorders that have an association with the presence of HLA-B27 include:
Juvenile rheumatoid arthritis (JRA), in which about 80% of affected patients are positive for HLA-B27.
Reiter’s syndrome (also known as reactive arthritis), with about 50-80% of patients are positive.
Isolated acute anterior uveitis, with about 40-70% of cases are positive.
HLA-B27 may also be present in patients with inflammatory bowel disease and with a range of other chronic conditions. While HLA-B27 has not been established as a cause of these disorders, there is a higher prevalence of this antigen in those affected.
