What is an HLA-B27 test?
Human leukocyte antigen B27 (HLA-B27) is a protein located on the surface of your white blood cells. An HLA-B27 test is a blood test that identifies HLA-B27 proteins.
Human leukocyte antigens (HLAs) are proteins commonly found on white blood cells. These antigens help your immune system identify the differences between healthy body tissue and foreign substances that may cause infection.
Although most HLAs protect your 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 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.
Why is the test ordered?
Monitoring disease progression
The presence of HLA-B27 is associated with certain autoimmune and immune-mediated diseases, including:
- ankylosing spondylitis, which causes inflammation of the bones in your spine
- reactive arthritis, which causes inflammation of your joints, urethra, and eyes, and sometimes lesions on your skin
- juvenile rheumatoid arthritis
- anterior uveitis, which causes swelling and irritation in the middle layer of your eye
A doctor may order the HLA-B27 test to monitor the progression of these and other autoimmune diseases.
For people with specific symptoms, the HLA-B27 test may be used along with other blood, urine, or imaging tests to confirm the diagnosis of an autoimmune disease. The symptoms that might prompt a doctor to order the test include:
- joint pain
- stiffness or swelling of your spine, neck, or chest
- inflammation of your joints or urethra accompanied by skin lesions
- recurring inflammation in your eye
Your doctor can order HLA antigen tests, including tests for HLA-B27, when you’re undergoing a kidney or bone marrow transplant. These tests can be used to ensure a suitable match between you and a donor.
How is the test administered?
The HLA-B27 test involves a standard blood draw. A healthcare provider in a doctor’s office or a clinical lab administers it. They usually take the blood sample from your arm using a small needle. Your blood is 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?
Some people may experience discomfort when their blood is drawn. You may feel pain at the puncture site during the test and mild pain or throbbing at the puncture site afterward.
Undergoing the HLA-B27 test carries minimal risks. All blood tests have the following risks:
- difficulty obtaining a sample, which results in multiple needle sticks
- excessive bleeding at the puncture site
- an accumulation of blood under your skin, called a hematoma
- an infection at the puncture site
How are the results interpreted?
A negative test indicates the absence of HLA-B27 in your blood.
However, if the test is negative, it doesn’t mean that you don’t have an autoimmune disorder. When making a final diagnosis, your doctor will consider all test results along with your symptoms. Sometimes people with autoimmune disorders don’t 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 doesn’t always mean 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.
The HLA-B27 blood test is one step in the process of diagnosing a potential autoimmune disorder. Neither positive nor negative results to the test should be taken as confirmation of whether you have an autoimmune disorder or not. Your doctor will talk to you about the next steps after you receive the results.