HLA-B27

This is a blood test to detect the presence of HLA-B27 on lymphocytes (white blood cells).

In the past, this test was performed using serum that specifically reacts with HLA-B27 on the cells (known as serologic tissue typing). Newer methods are now available that use genetic testing to identify the type of HLA-B27 in a particular individual. The HLA-B27 gene is designated as HLA-B*2701, HLA-B*2702, etc\

What is HLA-B27 used to diagnose

Spondyloarthropathies are chronic inflammatory disorders that include ankylosing spondylitis, Reiter's syndrome, reactive arthritis, psoriatic arthritis, Crohn disease, and ulcerative colitis. This group of disorders is associated with human leukocyte antigen (HLA) B27 suggesting a possible autoimmune etiology. The strength of the association with the HLA-B27 allele varies among the different spondyloarthropathies and among ethnic groups. The strongest association is with ankylosing spondylitis. HLA-B27 (alleles B*2701-B*2723) is present in >90% of Caucasians with ankylosing spondylitis compared to an 8% frequency in the general Caucasian population.

Ankylosing spondylitis is the most common inflammatory disorder of the axial skeleton. Men are affected 2-3 times more frequently than women. Disease onset typically occurs in young adulthood manifesting as lower back pain and/or stiffness progressing to chronic pain with marked axial immobility or deformity. Sacroilitis is the hallmark feature of this disorder. In addition, ocular involvement, most commonly acute uveitis, is seen in 40% of patients, while 60% of patients have asymptomatic irritable bowel disease.

DNA testing for detection of HLA-B27 is extremely accurate and considered the gold standard. Identification of HLA-B27 by DNA testing supports the diagnosis of ankylosing spondylitis in symptomatic individuals and a negative result excludes the diagnosis. Early detection of ankylosing spondylitis through genetic and radiographic testing may provide an opportunity for treatment before permanent limitation of spinal mobility.