What is an HLA-B27 Test?
Human leukocyte antigen B27 (HLA-B27) is a blood test that identifies a specific protein located on the surface of your white blood cells called human leukocyte antigen B27.
Human leukocyte antigens (HLAs) are proteins commonly found on white blood cells. These antigens help your immune system identify differences between healthy body tissue and foreign substances that may cause infection.
Although most HLAs protect the body from harm, HLA-B27 is a specific type of protein that contributes to immune system dysfunction. The presence of HLA-B27 on your white blood cells can cause your immune system to attack the healthy cells that contain it. When this occurs, it can result in an autoimmune disease, such as juvenile rheumatoid arthritis.
Why is the Test Ordered?
Monitoring Disease Progression
The presence of HLA-B27 is associated with a host of autoimmune diseases, including:
- ankylosing spondylitis (causes inflammation of the bones in the spine)
- reactive arthritis (causes inflammation of the joints, urethra, and eyes and sometimes lesions on the skin) juvenile rheumatoid arthritis
- anterior uveitis (causes swelling and irritation in the middle layer of the eye)
A doctor may order the HLA-B27 test to monitor the progression of these (and other autoimmune) diseases.
For patients with specific symptoms, the HLA-B27 test may be used in conjunction with other blood tests to confirm the diagnosis of an autoimmune disease. Symptoms that might prompt a doctor to order the test include:
- joint pain
- stiffness or swelling of the spine, neck, or chest
- inflammation of the joints and/or urethra accompanied by skin lesions
- recurring inflammation of the structures of the eye
HLA antigen tests, including tests for HLA-B27, are also ordered when a patient is undergoing a kidney or bone marrow transplant. These tests can be used to match donor tissue to an organ recipient.
How is the Test Administered?
The HLA-B27 test involves a standard blood draw. It is administered by a nurse or technician in a doctor’s office or clinical lab. The blood sample is usually extracted from the arm using a small needle. The blood will be collected in a tube and sent to a lab for analysis.
Most of the time, no special preparation is necessary. However, talk to your doctor to see if you need to stop taking any of your medications before the blood draw.
What are the Risks of the Test?
Patients may experience some discomfort when their blood is drawn. You may feel pain at the puncture site during the test and mild pain or throbbing there after the test.
The HLA-B27 test carries minimal risks. The following rare complications are common to all blood tests:
- difficulty obtaining a sample, resulting in multiple needle sticks
- excessive bleeding at the puncture site
- fainting or light-headedness
- accumulation of blood under the skin (hematoma)
- infection at the puncture site
Interpreting Your Results
Ideally, your test will be negative, indicating the absence of HLA-B27 in your blood. However, if the test is negative, it doesn’t mean that you absolutely do not have an autoimmune disorder. When making a final diagnosis, your doctor will consider all test results along with your symptoms. In some cases, patients with autoimmune disorders do not have HLA-B27 on their white blood cells.
If the test is positive, this means that HLA-B27 is present in your blood. Although a positive result may be cause for concern, the presence of the antigen does not always indicate that an autoimmune disorder will develop. Diagnosis of an autoimmune disorder must be made based on your symptoms and the results of all blood tests and diagnostic exams.