HLA-B27 Antigen

Does this test have other names?

Human lymphocyte antigen B27, human leukocyte A antigen, white blood cell antigens, histocompatibility leukocyte A antigen

What is this test?

This test looks for HLA-B27, an antigen, or protein, found on the surface of infection-fighting white blood cells. If you have HLA-B27, you may have an autoimmune disease. Autoimmune diseases occur when your immune system sees its own cells as foreign invaders and destroys them. The most common autoimmune disorders associated with HLA-B27 antigens are ankylosing spondylitis, a form of arthritis that affects the spine; juvenile arthritis, which occurs in children; and reactive arthritis, or Reiter's syndrome, a type of arthritis in the joints.

Your HLA antigens are unique to you and are determined by your genes. Therefore, this blood test is useful in paternity investigations.

Why do I need this test?

You might have this test if your doctor suspects that you have ankylosing spondylitis because of pain and stiffness in your back, neck, or chest. This is especially true if you are a man and have symptoms in your early 30s.

You also might have this test if you are undergoing an organ transplant of your kidney or bone marrow, for instance. Your donor's HLA antigens must match yours for the transplant to have a chance to be successful. You might have this test if someone needs to determine paternity.

What other tests might I have along with this test?

Your doctor also might order:

• Erythrocyte sedimentation rate, or ESR, which suggests inflammation

• C-reactive protein, which also can look for inflammation

• Joint X-rays or MRI

• Urine test

These tests can help confirm an autoimmune diagnosis if your HLA-B27 antigen test is positive.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Normal results are negative, which means you don't have HLA-B27 in your blood. A positive test means HLA-B27 was found in your blood. You may have a higher-than-average risk of developing or having certain autoimmune diseases, such as ankylosing spondylitis and reactive arthritis. If you are white, you are more likely to test positive for the HLA-B27 antigens than if you are of a different race.

If you need an organ or tissue transplant and your HLA antigens are not compatible with those of your donor, your body could reject the transplant.

In a paternity case, if the child or father has an unusual HLA genotype, paternity could be clear. If it's a common HLA genotype, the child could have many potential fathers.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

No other factors can affect your results.

How do I get ready for this test?

You don't need to prepare for this test.  But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.