Fever of unknown origin: focused diagnostic approach based on clinical clues from the history, physical examination, and laboratory tests.

The causes of fevers of unknown origin (FUOs) are diverse and may be the result of infectious rheumatic or inflammatory, neoplastic, or miscellaneous disorders. This article reviews the focused diagnostic approach to FUOs, emphasizing relevant history, physical examination, and selected laboratory tests using a clinical syndrome approach. Laboratory tests should be guided by the most likely diagnoses based on the presenting clinical syndrome. Considered in concert, nonspecific laboratory tests may provide important diagnostic clues. Using a sequential diagnostic approach, a focused evaluation diagnoses all but the rarest or most obscure causes of FUO.