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Legionella Antibody

Does this test have other names?

Legionnaires' disease antibody test, Legionella antibody assay

What is this test?

This test looks for an antibody that may be in your blood if you have Legionnaires' disease.

Legionnaires' disease is a type of pneumonia or serious lung infection caused by bacteria called Legionella.

Antibodies are proteins that your immune system makes to fight infection or foreign invaders. The bacteria and the disease get their name because of an outbreak that happened among people attending an American Legion convention in Philadelphia in 1976.

Why do I need this test?

You may need this test to see if your healthcare provider suspects that you have Legionnaires' disease. Or you may have this test if your provider thinks you have a milder form of infection known as Pontiac fever. Symptoms of Legionnaires' disease include:

  • High fever

  • Chills

  • Cough

  • Muscle aches

  • Headaches

Symptoms may begin 2 days to 2 weeks after you are exposed to the bacteria.

You may need this test again in several weeks to confirm your diagnosis or to see whether you have recovered.

What other tests might I have along with this test?

Your healthcare provider might also order a chest X-ray to diagnose pneumonia. He or she might also take a sample of your mucus or lung tissue for a culture test, and order a urine test to look for Legionella.

What do my test results mean?

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. 

Normal results are negative. This means no Legionella antibody was found in your blood. A positive result means that Legionella antibodies were found and that you may have Legionnaires' disease.

How is this test done?

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

Does this test pose any risks?

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. 

What might affect my test results?

If the test is done too early after you are infected, you may have a false-negative result because you may not yet have developed enough antibodies to the bacteria. 

How do I get ready for this test?

You don't need to prepare for this test. Be sure your healthcare provider 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. 

Medical Reviewers:

  • Fraser, Marianne, MSN, RN
  • Haldeman-Englert, Chad, MD