The cause of this fever is unknown. In some people the cause may never be known. Finding a cause may be delayed if there is:
- A common illness that does not have the usual symptoms
- An infection that is often hard to diagnose
- Illness with symptoms that only appear later
- Illness that may not show up on tests until later, called delayed positive test
- Genetic condition that causes fever (rare)
You will be asked about your symptoms and past health. A physical exam will be done. Your doctor may ask questions to look for possible causes. Questions may include:
- Have you traveled?
- Have you been hospitalized?
- Is your immune system damaged?
- What medicine are you taking?
- Have you been near anyone who has been ill?
- Have you ever been around someone with tuberculosis?
Tests to look for cause may include:
- Blood and urine tests
- CT scan
This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.
Edits to original content made by Denver Health.
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a (FUO; Pyrexia of Unknown Origin)
Family Doctor—American Academy of Family Physicians https://familydoctor.org
Healthy Children—American Academy of Pediatrics https://www.healthychildren.org
Caring for Kids—Canadian Paediatric Society http://www.caringforkids.cps.ca
Health Canada http://www.hc-sc.gc.ca
Cunha B, Lortholary O, et al. Review of fever of unknown origin: clinical approach. can be found in Am J Med 2015 Oct;128(10):1138. Accessed at: https://www.ncbi.nlm.nih.gov/pubmed/26093175.
Fever of unknown origin (FUO) in adults. EBSCO DynaMed website. Available at: https://www.dynamed.com/approach-to/fever-of-unknown-origin-fuo-in-adults/ . Updated January 13, 2017. Accessed February 6, 2020.
Varghese G, Trowbridge P, et al. Investigating and managing pyrexia of unknown origin in adults. BMJ 2010;341. Accessed at: https://www.ncbi.nlm.nih.gov/pubmed/22312655?dopt=Abstract.