Fever of unknown origin is a high body temperature with no clear cause, even though there has been at least one week of testing. The fever is present for at least three weeks.
The cause of this fever is unknown. In some people the cause may never be known.
Factors that may make it difficult to find a cause include:
- A common illness that does not have the usual symptoms
- Unusual illness, whose other symptoms appear later
- Person is unable to communicate about other symptoms such as someone in a coma
- Genetic condition that causes periodic fevers—very rare
Since the cause of FUO's is unclear, there are no specific factors that increase your chance of this fever.
A fever is considered
a temperature over 100.9 degrees Fahrenheit (38.3 degrees Celsius). It may be consistent or occur sporadically. A fever is a common symptom related to both trivial and serious health issues.
You may or may not have other symptoms that are caused by the underlying illness.
Your doctor will ask about your symptoms and medical history. A physical exam will be done. If there is no clear cause, your doctor will begin to narrow possibilities. The first step is to ask about your recent history such as:
- Were you traveling abroad?
- Were you hospitalized?
- Is your immune system damaged?
- What medicines are you currently taking?
Based on your history your doctor may then order some tests to look for possible causes. Tests may include:
- Blood, urine, and other body products testing
- Images of internal organs and structures with
CT scans, MRI
scans, or ultrasound
- Biopsy of suspicious tissue
Endoscopies to examine the inside of the lungs,
intestines, or sinuses
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There is no treatment for a FUO itself. Treatment for the fever may not be necessary since a fever is a normal part of your immune system. Lowering the fever with medication may make it harder for your body to fight the infection, if one is present. Your doctor may recommend medication to lower the fever if it is extremely high or causing other health related problems.
If an underlying condition is found it will be treated based on the condition.
Since the cause is unclear there are no steps to prevent FUO.
Roth A, Basello G. Approach to Adult Patient with Fever of Unknown Origin. Am Fam Physician. 2003 Dec 1;68(11):2223. Available at: . Accessed May 20, 2013.
Fever of Unknown Origin (FUO). EBSCO DynaMed website. Available at:
. Updated November 13, 2012. Accessed May 20, 2013.
Gelfand JA, Callahan MV. Fever of unknown origin. In: Kasper DL, Braunwald E, Fauci A, Hauser S, Longo D, Jameson JL.
Harrison's Principles of Internal Medicine. 16th ed. New York: McGraw-Hill; 2005: 16-121.
Goldman L, Ausiello D, eds.
Cecil Textbook of Internal Medicine.
23rd ed. Philadelphia, PA: Saunders; 2008.
Last reviewed May 2013 by Michael K. Mansour, MD, PhD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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