What are key features of fever of unknown origin (FUO)?

Updated: Mar 01, 2018
  • Author: Sandra G Gompf, MD, FACP, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Key features of fever of unknown origin (FUO), also known as pyrexia of unknown origin (PUO), are as follows:

  • Unexplained fevers are worrisome to patients and clinicians, but most persistent fevers are diagnosed, and often within one week of hospital evaluation or 3 outpatient visits.
  • Most fevers that persist beyond this period are caused by common conditions presenting uncommonly.
  • Hundreds of conditions may cause FUO. While infections remain a significant cause, most FUOs in the developed world are caused by noninfectious inflammatory disorders, with malignancy a much smaller percentage. Infection is likely to evolve with increased global travel and use of immunomodulating drugs.
  • The differential diagnoses of FUO depend on and continue to evolve based on regional factors, exposures, and available diagnostic tools.
  • A significant percentage of FUO cases are caused by miscellaneous conditions, and there is no standard algorithm for evaluating FUO. The approach to diagnostic study is best guided by ongoing assessment for historical, physical, and basic laboratory clues. Following clues and beginning with the least invasive evaluation avoids unnecessary harm and cost to the patient.
  • Physical examination in FUO should pay special attention to skin, eyes, lymph nodes, liver, and spleen.
  • It is reassuring that most cases of FUO that remain undiagnosed despite intensive evaluations have a good long-term prognosis and resolve within a year.

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