Fever of unknown origin (FUO) is a higher body temperature with no clear cause, even though there has been at least 1-2 weeks of testing.
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 symptomsIllness with other symptoms that may appear laterIllnesses that may have a delayed positive testPerson is unable to communicate about other symptoms such as an infant or someone in a comaGenetic condition that causes periodic fevers—rare
Since the cause of FUO is unclear, there are no specific factors that increase your chance of this fever.
A fever is generally considered
a temperature over 101 degrees Fahrenheit (38.3 degrees Celsius) but the exact number can vary. A fever of unknown origin may be consistent or occur sporadically.
The fever may also be accompanied by chills, sweating, or other symptoms that are caused by the underlying illness.
You will be asked 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. You may be asked the following: Were you traveling abroad?Were you hospitalized?Is your immune system damaged?What medications are you currently taking?
Your bodily fluids may be tested. This can be done with: Blood testsUrine testsBiopsy
Images may be taken of your bodily structures. This can be done with: X-raysCT scanMRI scanUltrasound
The inside of your lungs, intestines, or sinuses may be examined. This can be done with endoscopy.
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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 advise medication to lower the fever if it is extremely high or causing other health-related problems.
If an underlying condition is found, treatment will be based on that illness.
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;68(11):2223.
Fever of unknown origin (FUO) in adults. EBSCO DynaMed website. Available at:
http://www.ebscohost.com/dynamed. Updated August 29, 2014. Accessed September 25, 2014.
Last reviewed August 2015 by David Horn, MD
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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