Overview

Definition

Fever of unknown origin (FUO) is a high body temperature with no clear cause, even though there has been at least 1-2 weeks of testing.

Causes

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
  • Illnesses with other symptoms that may appear later
  • Illnesses that may have a delayed positive test
  • Inability to communicate about other symptoms, such as an infant or someone in a coma
  • Genetic conditions that causes periodic fevers—rare

Risk Factors

Since the cause of FUO is unclear, there are no specific factors that increase your chance of this fever.

SymptomsandDiagnosis

Symptoms

A fever is generally considered a temperature over 101°F (38.3°C), 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.

Diagnosis

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 and tissues may be tested. This can be done with:

  • Blood tests
  • Urine tests
  • Biopsy

Images may be taken of your bodily structures. This can be done with:

  • X-rays
  • CT scan
  • MRI scan
  • Ultrasound

The inside of your lungs, intestines, or sinuses may be examined. This can be done with endoscopy.

Endoscopy
Endoscope in stomach
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Treatments

Treatment

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.

Prevention

There are no current guidelines to prevent FUO since the cause is not known.

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

Edits to original content made by Denver Health.

a (FUO; Pyrexia of Unknown Origin)

RESOURCES

Family Doctor—American Academy of Family Physicians https://familydoctor.org 

Healthy Children—American Academy of Pediatrics https://www.healthychildren.org 

CANADIAN RESOURCES

Caring for Kids—Canadian Paediatric Society http://www.caringforkids.cps.ca 

Health Canada http://www.hc-sc.gc.ca 

References

Roth A, Basello G. Approach to adult patient with fever of unknown origin. Am Fam Physician. 2003;68(11):2223.

Fever in the returning traveler. EBSCO DynaMed Plus website. Available at:  http://www.dynamed.com/topics/dmp~AN~T905783/Fever-in-the-returning-traveler  . Updated February 14, 2017. Accessed August 14, 2017.

Fever of unknown origin (FUO) in adults. EBSCO DynaMed Plus website. Available at:  http://www.dynamed.com/topics/dmp~AN~T116707/Fever-of-unknown-origin-FUO-in-adults  . Updated January 13, 2017. Accessed August 14, 2017.