American Board of Internal Medicine (ABIM) Certification Practice Exam

What defines fever of unknown origin (FUO)?

1. A temperature greater than 37.5 °C for at least 2 weeks

2. A temperature greater than 38.3 °C for at least 3 weeks

3. A temperature greater than 39.0 °C for at least 1 week

4. A temperature greater than 100.0 °F for at least 5 days

The correct answer is: A temperature greater than 38.3 °C for at least 3 weeks

Fever of unknown origin (FUO) is a clinical condition characterized by a sustained fever that remains undiagnosed after thorough evaluation. The defining criteria for FUO include a temperature greater than 38.3 °C (101 °F) for at least 3 weeks, which aligns with the correct answer. This definition is critical in the clinical setting because it helps physicians categorize and manage patients presenting with prolonged fever without an apparent cause. Patients typically undergo detailed histories, physical examinations, laboratory tests, and imaging studies to identify the etiological factors behind the fever. The duration and degree of the fever are essential criteria that set FUO apart from other febrile conditions, ensuring that a serious underlying illness is not overlooked. The other definitions do not match the established criteria for FUO. For instance, a temperature greater than 37.5 °C for 2 weeks or greater than 39.0 °C for 1 week does not meet the standard definition, and a temperature greater than 100.0 °F for 5 days is also insufficient in duration to qualify as FUO. Understanding these parameters is crucial for appropriate diagnosis and treatment of unexplained fevers.