Fig. 1.

Proposed algorithm for a diagnostic approach to prolonged fever: Patients with a febrile illness ≥37.8 °C (orally) for ≥1 week will undergo a basic clinical workup during Phase #1 of the study (top box). If no diagnosis can be established during this initial phase, or no clue regarding a potential differential diagnosis can be made, patients enter Phase #2. There an ¹⁸FDG-PET/CT will be performed to elicit further diagnostic clues (bottom box). FUO fever of unknown origin