Fever of Unknown Origin (FUO)

The evaluation of Fever of Unknown Origin (FUO) begins with a thorough medical history and physical examination. Doctors check for recent infections, vaccinations, travel, medication use, and family health conditions.

Initial tests

• Blood tests
• Urine tests
• X-rays and ultrasound
• Blood and urine cultures

If the cause is still unclear, further tests may be needed:

• Autoimmune or infection-related blood tests
• Echocardiography
• CT or PET scans
• Bone marrow or tissue biopsy

In most cases, doctors avoid giving antibiotics or steroids right away, as these can make diagnosis harder. Careful follow-up is often the best approach, especially when the child appears well.

Management of FUO is guided by the underlying cause, once identified. Until then, the primary approach is supportive care and cautious observation. Empirical treatments—especially antimicrobials or immunosuppressants—should be avoided unless there are specific clinical indications, as premature therapy can suppress diagnostic findings and delay appropriate treatment. If a definitive diagnosis is made, disease-specific treatment should be initiated promptly, such as antibiotics for occult bacterial infections, corticosteroids or biologics for inflammatory conditions like sJIA, or chemotherapy for malignancies. In undiagnosed cases where the patient remains clinically stable, ongoing monitoring with periodic reassessment is often the best course. The goal is to avoid both under-investigation and over-intervention while maintaining a high index of suspicion and readiness to intervene when new clinical clues emerge.