Fever of Unknown Origin

Head | General Practice | Fever of Unknown Origin (Symptom)


Fever of unknown origin (FUO) refers to a condition in which the patient has an elevated temperature but despite investigations by a physician no explanation has been found. The presence of fever greater than 38. 3C (101F) off and on for more than three weeks without a specific cause identified for the fever.


Extensive diagnostic testing can determine the cause in the majority of cases of FUO. It may be related to infections such as HIV or other viral infections, cancers, or chronic inflammatory diseases such as sarcoidosis.

Extrapulmonary tuberculosis is the most frequent cause of FUO. Drug-induced hyperthermia, as sole symptom of an adverse reaction to medication, should always be considered. Disseminated granulomatoses such as Tuberculosis, Histoplasmosis, Coccidioidomycosis, Blastomycosis and Sarcoidosis are also associated with FUO. Lymphomas are the most common cause of FUO in adults.