A high temperature without a clear cause is given the term fever of unknown origin (FUO). A FUO is an intermittent temperature of at least 101°F. It has to have been noted for over three weeks. It also has to have at least a week’s worth of attempts to find the cause.
There are many rare causes of a high temperature. The following list includes just a few of the uncommon causes:
Extrapulmonary (located elsewhere than in the lungs)
Atypical tuberculosis (relatives of the common germ)
If you experience any of these, do not assume it is due to a FUO. A fever is a very common indication of many problems. They can be both serious and trivial. If you experience any one of them, see your doctor.
Elevated temperature by thermometer reading
Aching all over
Your doctor will ask about your symptoms and medical history. A physical exam will be done. You can help by taking your temperature several times a day. Your doctor may refer you to a specialist.
The first efforts after the usual evaluation will be to narrow the possibilities. This is done by examining the circumstances under which the fever began. Were you traveling abroad? Were you hospitalized? Is your immune system damaged, for example by AIDS? What medications are you currently taking?
Many different tests may be indicated at some point including:
Exhaustive studies of blood, urine, and all other bodily products
Exhaustive imaging studies: x-rays, CT and MRI scans, ultrasound examinations
Nuclear medicine studies
Endoscopies (lungs, stomach and intestines, sinuses, etc)
(samples taken by knife or needle) of suspect tissues
Beers MH, Berkow R. Biology of infectious disease. In:
The Merck Manual
. 17th ed. Merck & Co: West Point, PA; 1999.
Gelfand JA, Callahan MV. Fever of unknown origin. In: Kasper DL, Braunwald E, Fauci A, Hauser S, Longo D, Jameson JL.
Harrison's Principles of Internal Medicine
. 16th ed. New York: McGraw-Hill; 2005: 16-121.
Roth AR, Basello GM. Approach to the adult patient with fever of unknown origin. Dec 1, 2003. American Family Physician website. Available at:
. Accessed September 14, 2005.
Please be aware that this information is provided to supplement the care
provided by your physician. It is neither intended nor implied to be a
substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER
IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the
advice of your physician or other qualified health provider prior to
starting any new treatment or with any questions you may have regarding a