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.
The commonest cause of fever is infection, in one study of hospital inpatients accounting for ~70% cases . 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).
- infection (~70% cases)
- medication: drug fever
- inflammatory disease: many diseases, including granulomatous (e.g. sarcoidosis), vasculitides, and autoimmune (e.g. hepatitis)
- recreational drugs, e.g. MDMA (ecstasy), cocaine, amphetamines, LSD, mephedrone
- brain insult: trauma, ischemia, cerebral hemorrhage
- endocrine (rare): thyrotoxicosis, pheochromocytoma, hypoadrenalism