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Fever Undiagnosed

A fever of unknown origin (FUO) is a fever of at least 101°F (38.3°C) that lasts for more than three weeks or occurs frequently without explanation. Even when a doctor can’t determine the cause of the fever at first, a diagnosis is a step toward treating it.

Some of the signs and symptoms of type 1 and type 2 diabetes are:

  • Increased thirst
  • Frequent urination
  • Extreme hunger
  • Unexplained weight loss
  • Presence of ketones in the urine (ketones are a byproduct of the breakdown of muscle and fat that happens when there's not enough available insulin)
  • Fatigue
  • Irritability
  • Blurred vision
  • Slow-healing sores
  • Frequent infections, such as gums or skin infections and vaginal infections


Recognizing the type of FUO helps a physician find its cause. Causes of FUO can be categorized as any of the following:

Infection: tuberculosis, mononucleosis, Lyme disease, cat scratch fever, endocarditis, and others
Inflammation: lupus, rheumatoid arthritis, inflammatory bowel disease, and others
malignancy: lymphoma, leukemia, pancreatic carcinoma, and other cancers and sarcomas
miscellaneous: fevers caused by drug use or abuse, hyperthyroidism, hepatitis, and factors that don’t fit into other categories
A person with a FUO is given several clinical tests to narrow down the FUO’s classification. Diagnosis of the FUO can also draw attention to an otherwise undiagnosed condition.


FUO may be accompanied by other symptoms that can help doctors determine the underlying cause.

Typical symptoms of a fever include:

  • a temperature that exceeds 100.4°F (38°C) for babies or 99.5°F (37.5°C) for children and adults
  • sweating
  • chills
  • headaches

Other symptoms that typically accompany fever include:

  • body or joint aches
  • weakness
  • sore throat
  • fatigue
  • cough
  • rash
  • sinus congestion