Fever (synonyms: Fever; Status febrilis; ICD-10-GM R50.-: Fever of other and unknown cause) refers to an increase in body temperature that is due to a set point adjustment in the thermoregulatory center of the hypothalamus (part of the diencephalon). Fever is the increase in surface temperature of > 38.0 °C or core temperature of > 38.3 °C.Hyperthermia must be distinguished from fever. This is the most severe form of fever of non-infectious origin. In this case, an elevated body temperature is present, although no set point adjustment has taken place. Hyperthermia is said to occur when body temperature is ≥ 40 °C and neurologic symptoms are present. Body temperature is lowest in the early morning hours and highest in the early evening hours. Normal body temperature also varies with age (infants have a temperature approximately 0.5 °C higher than children and adults) and with activity level. In addition, in women the temperature also varies by about 0.5 °C over the monthly cycle (basal body temperature). The mean temperature measured orally (in the mouth) is 36.8 °C. The mean temperature measured rectally (in the anus) is 37.2 °C. Fever is a nonspecific symptom that indicates the presence of a disease, but does not allow conclusions to be drawn about its character or its cause and localization. A feverish increase in temperature (38-41 °C) serves to accelerate the body’s own metabolic processes and thus promotes the body’s defense reactions. Furthermore, fever leads to inhibition of replication (“multiplication”) of bacteria and viruses. Fever is triggered by so-called pyrogens or an immune reaction originating from the body itself. Pyrogens originate from bacteria, viruses, fungi or parasites (exogenous pyrogens) or are produced by defense cells or messenger substances (interleukin-1, tumor necrosis factor (TNF), interferons) of the own organism (endogenous pyrogens). The fever leads to a set point increase and triggers the typical shivering and muscle trembling (chills). For the production and maintenance of fever, the body increases its energy requirement by about 20% (by increasing the body temperature by 2-3 °C). Classification of fever
| Subfebrile temperature | 37,5 – 38 °C |
| Mild fever | 38,1 – 38,5 °C |
| Moderate fever | – 39 °C |
| High fever | 39,1 – 39,9 °C |
| Very high fever | > 40,0 °C |
Exitus (death) due to denaturation (protein coagulation) in the body at 42.6 °C.
The following types of fever are described:
- Infectious fever (fever associated with an infectious disease): in patients in an intensive care unit, infections are the cause of temperature elevation in 50% of cases.
- Drug fever (drug-induced fever; fever associated with taking a drug; English : Drug Fever)
- Postoperative fever (fever that occurs after surgery).
- Transfusion fever (fever associated with a transfusion).
- Tumor fever (fever associated with a tumor disease); see also under “Symptoms – complaints”.
- “Fever of Unknown Origin” (FUO; fever of unclear genesis/cause). One speaks of it when
- In adults, a body temperature of over 38.3 °C is measured several times within three weeks without success in finding the cause of the fever within a week.
- In children, fever without a known focus (focus) persists for more than eight days.
Forms of fever progression:
- Stage incrementi (increase in fever).
- Slow,
- Staircase fast, possibly with chills.
- Stage fastigium (fever pitch).
- Stage decrementi (fever decrease)
- Lytic, meaning normal (lysis = slow decrease of fever).
- Critical, which means: cold, sticky sweat (crisis = rapid drop in fever).
Relevant types of fever see below classification. Causes of fever in hospitalized patients:
- 54% of cases there is an infection
- 12.8% non-infectious inflammatory disease
- 7.1 % neoplasia
- 14.6% other cause (including drugs).
- 11.5% of cases could not be diagnosed
Fever can be a symptom of many diseases (see under “Differential diagnoses”). The prognosis depends on the cause of the fever.
