Fever of Unknown Origin
Fever of unknown origin (FUO) refers to elevated body temperature for which a cause is not found after basic medical evaluation.
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What Is a Fever of Unknown Origin?
A fever of unknown origin (FUO) is a fever of at least 101
degrees Fahrenheit (38.3 degrees Celsius) that either lasts for more than three
weeks or occurs frequently without explanation. Even though a doctor cannot
initially determine the cause of the fever, a diagnosis of FUO is a step toward
finding a cure.
Types of Fever of Unknown Origin
There are four classifications of FUO: classic, nosocomial,
immune-deficient, and HIV-associated.
- Classic FUO affects previously
healthy people. It is defined as an unexplained fever that lasts for three
weeks. Infection or neoplasms such as leukemia may cause classic FUO. Other
disorders, such as diseases that affect connective tissue, can also be the
- People with nosocomial FUO
appear to acquire fever as a result of hospitalization. They are admitted
for a reason other than fever and then begin to run an unexplained fever.
Common causes include pulmonary embolism, septic thrombophlebitis,
enterocolitis, and sinusitis.
- Immune-deficient FUO occurs
in people with compromised immune systems. This puts them at an increased
risk of infection. This can occur because of chemotherapy treatment.
- HIV itself can cause fevers.
In addition, HIV makes a patient susceptible to infections that may cause
What Causes a Fever of Unknown Origin?
FUO has four primary types of causes. Recognizing the type
of FUO helps a physician determine its cause. Each type of cause includes
tuberculosis, mononucleosis, Lyme disease, cat scratch fever, and others
lupus, rheumatoid arthritis, inflammatory bowel disease, and others
lymphoma, leukemia, pancreatic carcinoma, other cancers, and sarcomas
fevers that are caused by drug use or abuse, are the result of
hyperthyroidism or hepatitis, or don’t fit into other categories.
A patient with a FUO will be given a variety of clinical
tests to narrow down the FUO’s classification. Diagnosis of the FUO can be
useful in drawing attention to an otherwise undiagnosed condition.
What Is the Treatment for a Fever of Unknown Origin?
Treatment for a FUO varies greatly and depends on the
underlying cause. In about 30 percent of cases, the patient is discharged
without a definitive diagnosis. In many such cases, FUO resolves itself in
Maureen Ash and Ana Gotter
Medically Reviewed by:
Aug 27, 2013
Published By: Healthline Networks, Inc.