Last reviewed 01/2018
Fever is a rise in body temperature above the normal daily variation, greater than 37.8'C orally or 38.2'C rectally. There is a diurnal variation, lowest in the early morning and highest in the late afternoon and evening ('teatime to bedtime'). It may be caused by infection, inflammation, neoplasm or an immunologically mediated disorder.
The pattern of fever may be intermittent (swings between raised and normal) or remittent (when the temperature does not return to normal).
Exogenous and endogenous pyrogens cause the hypothalamus to reset the body's thermostat and bring into play mechanisms that raise and maintain a higher than normal temperature. Shivering and rigors are part of this mechanism.