Last revised by Daniel J Bell on 13 Nov 2023

Pyrexia (or fever) is a clinical sign, indicated by an abnormally elevated core body temperature, which is defined by several medical societies as ≥38.3°C (≥≈101°F). The temperature elevation may be persistent or episodic. If the body temperature is greater than 41.5°C - a rare phenomenon - it is known as hyperpyrexia. Fevers may be accompanied by night sweats.

The commonest cause of fever is infection, in one study of hospital inpatients accounting for ~70% cases 1. Other frequent causes are inflammatory disease, malignancies and medication-related fevers. Pyrogenic is the term used for anything that causes pyrexia (cf. pyogenic: pus-forming). A treatment that directly lowers the body temperature is an antipyretic. When the cause of fever remains unexplained it is termed pyrexia of unknown origin (PUO).



Treatment and prognosis

The proactive treatment of pyrexia is an area of contention as many have stated that the fever is part of the body's immune response to infection. There is also evidence lacking that bringing a fever down improves outcomes.

Physical measures such as removing excess clothing and tepid baths are often the initial measures tried.

Drugs in the form of antipyretics may also be used, agents include aspirin (not in children), acetaminophen and NSAIDs

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