To be classified as a fever of unknown origin (FUO), the body temperature must be above 103.5°F (39.7°C) for longer than a few days, with no obvious underlying cause based on history and physical examination. A fever is beneficial to the body, but if a fever remains above 106°F (41.1°C) for more than a few days several consequences occur within the body and can be life threatening. If your pet has a fever, your veterinarian will perform a thorough physical examination, perform diagnostic blood tests, urine culture, and possibly other diagnostic tests. Antibiotics are often prescribed. Cats that have persistent fever or a fever that waxes and wanes must undergo a thorough work-up so that the cause of fever can be discovered and treated before irreversible damage occurs.