Human lymphocyte antigen B27, human leukocyte A antigen, histocompatibility leukocyte A antigen

This test looks for HLA-B27, which are proteins called antigens. These are found on the surface of white blood cells that are fighting infection. If you have HLA-B27, you may have an autoimmune disease. An autoimmune disease is when your immune system attacks your own cells. The most common autoimmune disorders connected with HLA-B27 antigens are:

• Ankylosing spondylitis, a form of arthritis that affects the spine.
• Juvenile arthritis, which occurs in children.
• Reactive arthritis, a type of arthritis in the joints.

Your HLA antigens are unique to you. They are determined by your genes.

You may need this test if your doctor thinks that you have ankylosing spondylitis or another autoimmune disease. Ankylosing spondylitis can cause pain and stiffness in your back, neck, or chest. This is more common if you are a man and have symptoms in your early 30s.

You also may need this test if you are having an organ or tissue transplant. For example, this may be a donor kidney or bone marrow. Your donor's HLA antigens must match yours for the transplant to have a chance to be successful.

If your HLA-B27 antigen test is positive, you may need other tests to help confirm a diagnosis of an autoimmune disease. You may have tests, such as:

• Erythrocyte sedimentation rate (ESR), which may show you have inflammation.
• C-reactive protein, which also can look for inflammation.
• Joint X-rays or MRI.
• Urine test.

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your doctor what your test results mean for you.

A negative result means you don't have HLA-B27 in your blood. A positive result means HLA-B27 was found in your blood. You may have a higher-than-average risk of certain autoimmune diseases, such as ankylosing spondylitis and reactive arthritis.

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.

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand.

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.

No other factors can affect your results.

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 illegal drugs you may use.