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What is Fever of Unknown Origin? Fever with No Other Symptoms

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Fever of unknown origin or FUO is a chronic fever for which no cause can be conclusively identified. There are three criteria that define FUO and this includes :

  1. A persistent or recurrent body temperature of 38.3C (101F) or more,
  2. A fever continuing for more than 3 weeks,
  3. No conclusive diagnosis of the cause of the fever despite 3 days of inpatient care or 2 outpatient visits.

Pyrexia with No or Few Symptoms

Non-specific Fever Tests

A diagnosis of a specific medical condition is made upon the clinical presentation, which are the signs evident to the doctor and symptoms reported by the patient, along with a medical history. Investigations confirm the diagnosis and allows a doctor to assess the severity of the condition.

The presence of a fever with no other symptoms or vague and transient symptoms is referred to as a non-specific fever. In this instance, a diagnosis is difficult to make without further investigation. Some of the investigations that would be considered in the event of a non-specific fever include:

  • White blood cell (WBC) count and/or complete blood count (CBC)
  • Sputum test
  • Throat culture
  • Urinalysis
  • Stool test
  • Lumbar puncture
  • Chest x-ray

Other tests may be considered based on the patient’s medical, travel, occupational, sexual and family history. Recreational habits, drug usage (prescription/narcotic), lifestyle and nutrition as well as vector exposure (animal/insect contact, bites and stings). Refer to Traveler’s Fever, Drug Fever and Fever after Bites and Stings for more information on these aspects of a fever.

If no conclusive diagnosis can be reached after the clinical evaluation and investigations, the fever may be referred to as a fever of unknown origin (FUO). A factitious fever is where a patient manipulates the body temperature readings to record higher levels than is actually present and this has to be excluded as a possible cause of a fever of unknown origin.

Related Articles

  1. What is a Fever (Pyrexia)? Normal and High Body Temperature
  2. Sudden Fever – Causes of Acute Fever in Adults
  3. Childhood Fever – Causes of Fevers in Babies (Infants), Children

Article reviewed by Dr. Greg. Last updated on July 20, 2010