Please note: This information was current at the time of publication but now may be out of date. This handout provides a general overview and may not apply to everyone. 

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Am Fam Physician. 2014;90(2):online

See related article on febrile illness and fever of unknown origin in adults.

What is a fever of unknown origin?

This is a fever of 101°F (or 38.3°C) or higher that lasts for more than three weeks without a clear reason.

What causes it?

Causes may include infection, cancer, or an inflammatory disease (such as lupus, rheumatoid arthritis, or temporal arteritis). Other possible causes include certain medicines, thyroid swelling, or blood clotting disorders.

What information will my doctor need?

Your doctor will ask for:

  • A personal and family medical history

  • Places you've traveled (in the United States and overseas)

  • Medicines you've taken (including herbal and over-the-counter)

  • Contact you've had with sick people or animals

What tests will my doctor do?

Your doctor will test your blood and urine. He or she may order some basic imaging to get pictures of your chest or stomach, such as with an x-ray or ultrasound. There may be other tests based on your physical exam.

What if my doctor can't find a cause?

Most people who have a fever of unknown origin will get better or have a very mild illness. If a cause is not found, your doctor may talk with other doctors for another opinion.

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