Fever of unknown origin (FUO)

1. Big picture

Fever of unknown origin (FUO) is not “any fever without diagnosis today.” It is a persistent, documented fever that remains unexplained after an appropriate initial evaluation.

The examiner wants to hear a structured diagnostic approach, not random testing:

Confirm true fever
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Check duration and pattern
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Look for diagnostic clues in history + repeated physical examination
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Basic labs + cultures + chest imaging + urine testing
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Targeted tests based on clues
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CT / echocardiography / PET-CT / biopsy when indicated
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Avoid blind antibiotics or steroids unless unstable or strongly indicated

Most adult FUO cases fall into four groups: infection, malignancy, noninfectious inflammatory disease, and miscellaneous causes. Some remain undiagnosed and may resolve spontaneously. ([AAFP][1])

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