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 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 those otherwise healthy cells. 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 certain autoimmune
- ankylosing spondylitis, which causes inflammation
of the bones in the spine
- reactive arthritis, which causes inflammation of
the joints, urethra, and eyes, and sometimes lesions on the skin
- juvenile rheumatoid arthritis
- anterior uveitis, which 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 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
- joint pain
- stiffness or swelling of the spine, neck, or
- inflammation of the joints or urethra
accompanied by skin lesions
- recurring inflammation in the 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 match a donor’s tissue to the person receiving the kidney or
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. The
blood sample is usually taken 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?
Some people 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 at the puncture site after the test.
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 the skin called a
- an infection at the puncture site
Interpreting Your Results
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.