Fever of unknown origin
BMJ 2025; 388 doi: https://doi.org/10.1136/bmj-2024-080847 (Published 06 January 2025) Cite this as: BMJ 2025;388:e080847
- William F Wright, assistant professor1,
- Samuel C Durso, professor of medicine2,
- Colleen Forry, patient author3,
- Chantal P Rovers, professor of medicine4
- 1Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- 2Division of Geriatric Medicine and Gerontology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- 3Patient author, Lancaster, Pennsylvania, USA
- 4Department of Internal Medicine, Radboud University Medical Center, Nijmegen, the Netherlands
- Correspondence to: W F Wright wwrigh19{at}jhmi.edu
What you need to know
Fever of unknown origin is a clinical syndrome, and updated criteria (based on international consensus) are a raised temperature on several occasions with a prolonged illness in an immunocompetent patient and uncertain diagnosis on completion of a recommended set of minimal laboratory and imaging studies
Causes can be classified as infections, non-infection inflammatory disorders, neoplasms, miscellaneous conditions, and undiagnosed illnesses, and they vary with geographic region and patient’s age
Incorporate travel history when evaluating potential causes
It is more often explained by a common disease with an atypical presentation rather than by a rare disease
Consider early referral to a specialist for patients with confirmed fever, with or without elevated inflammatory markers, who remain undiagnosed in a generalist setting
Fever of unknown origin (also known as fever of undetermined origin or pyrexia of unknown origin) is often a debilitating clinical syndrome. Patients with this syndrome present to medical practitioners across all levels of health care, including general practice, emergency department, and secondary care services, across all geographic areas.12345 There are limited epidemiological data on this syndrome, and no data related to primary care presentations. However, in two retrospective cohort studies from Japan and Italy, prevalence of fever of unknown origin in secondary care ranged from 1.9% to 2.9% in 9830 hospitalised patients.34
This article outlines the current diagnostic defining criteria, causes, and evaluation strategies, including newer diagnostic methods that have emerged over the past 20 years. We also outline management recommendations among immunocompetent adult patients with prolonged unexplained febrile conditions.6789
What is fever of unknown origin?
Fever of unknown origin is a diagnosis based on a set of clinical, laboratory, and radiographic criteria.67101112 It is a syndrome characterised by a prolonged febrile illness with a set of medical signs and …
Log in
Log in using your username and password
Log in through your institution
Subscribe from £184 *
Subscribe and get access to all BMJ articles, and much more.
* For online subscription
Access this article for 1 day for:
£50 / $60/ €56 (excludes VAT)
You can download a PDF version for your personal record.