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Pathophysiology and treatment of fever in adults

Reuven Porat, MD
Charles A Dinarello, MD
Section Editor
Peter F Weller, MD, MACP
Deputy Editor
Anna R Thorner, MD


Fever, an elevation in core body temperature above the daily range for an individual, is a characteristic feature of most infections but is also found in a number of noninfectious diseases such as autoimmune and autoinflammatory diseases. Definitions of normal body temperature, the pathophysiology of fever, the role of cytokines, and the treatment of fever in adults will be reviewed here. Fever of unknown origin in adults, drug fever, and the treatment of fever in infants and children are discussed separately. (See "Approach to the adult with fever of unknown origin" and "Etiologies of fever of unknown origin in adults" and "Drug fever" and "Fever in infants and children: Pathophysiology and management".)


Normal body temperature varies over the course of the day, controlled in the thermoregulatory center located in the anterior hypothalamus. The body is normally able to maintain a fairly steady temperature because the hypothalamic thermoregulatory center balances the excess heat production, derived from metabolic activity in muscle and the liver, with heat dissipation from the skin and lungs. However, faced with environmental extremes, humans cannot maintain the narrow daily variation of body temperature without the aid of clothing and protective environments [1].

Peripheral methods of monitoring temperature (tympanic membrane, temporal artery, axillary, and oral thermometry) are not as accurate as central methods (pulmonary artery catheter, urinary bladder, esophageal, and rectal thermometry) [2], but central methods are less practical than peripheral methods.

There is increasing interest in circadian rhythms in humans and the genes that regulate daily oscillations in body temperature. Although it is well established that women in the luteal (post-ovulatory) phase have higher body temperature, the amplitude of the circadian rhythm for body temperature is the same as in men [3]. In 1992, a detailed study of the range of oral temperature readings in 148 healthy men and women aged 18 to 40 was reported using over 700 measurements [4]. Oral temperatures in the cohort ranged from 35.6°C (96.0°F) to 38.2°C (100.8°F) with a mean of 36.8 ± 0.4°C (98.2 ± 0.7°F). Low levels occurred at 6 AM and higher levels at 4 to 6 PM. The maximum normal oral temperature at 6 AM is 37.2°C (98.9°F), and the maximum level at 4 PM is 37.7°C (99.9°F), both values defining the 99th percentile for healthy subjects. From these studies, a morning reading >37.2°C (98.9°F) or an afternoon temperature of >37.7°C (99.9°F) would be considered a fever. Rectal temperatures are generally 0.6°C (1.0°F) higher than oral readings. Oral readings are lower probably because of mouth breathing, which is particularly important in patients with respiratory infections and rapid breathing. Temperature measurements from the lower esophagus reflect core temperature, and tympanic membrane temperature readings are also close to core temperature.

The normal daily temperature variation is typically 0.5°C (0.9°F). However, in some individuals recovering from a febrile illness, this daily variation can be as high as 1.0°C. During a febrile illness, daily low and high temperature readings are maintained but at higher levels.

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Literature review current through: Nov 2017. | This topic last updated: Dec 20, 2016.
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