High or persistent fever: Anything 103 degrees Fahrenheit or higher warrants an immediate trip to the doctor, without exception. A low-grade fever (somewhere around 100 degrees) for several weeks with no obvious cause should also be checked out.
What it might be: Fever is part of your body’s infection-fighting defenses, but an extremely high fever may signal a severe illness, from a urinary tract infection and pneumonia to endocarditis (inflammation of the heart lining) and meningitis. A persistent low-grade fever could be a sign of a sinus infection or of some cancers, such as lymphoma and leukemia. Other possibilities include a viral infection, which depending upon the bug and general health of the person might require hospitalization.
