Fever variations in body temperature

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


There are many variations in normal body temperature, and this needs to be considered when measuring fever.

Variations in Body Temperature

Body temperature normally fluctuates over the day, with the lowest levels at 4 a.m. and the highest at 6 p.m. Therefore, an oral temperature of 37.5°C (99.5°F) would strictly be a fever in the morning, but not in the afternoon. Normal body temperature may differ as much as 0.4°C (0.7°F) between individuals or from day to day. The values given are for an otherwise healthy, non-fasting adult, dressed comfortably, indoors, in a room that is kept at a normal room temperature, during the morning, but not shortly after arising from sleep. Furthermore, for oral temperatures, the subject must not have eaten, drunk, or smoked anything in at least the previous fifteen minutes.

In women, temperature differs at various points in the menstrual cycle, and this can be used for family planning (although it is only one of the variables of temperature). Temperature is increased after meals, and psychological factors (like the first day in the hospital) also influence body temperature.

There are different locations where temperature can be measured, and these differ in temperature variability. Tympanic membrane thermometers measure radiant heat energy from the tympanic membrane (infrared). These may be very convenient, but may also show more variability.

Children develop higher temperatures with activities like playing, but this is not fever because their set-point is normal. Elderly patients may have a decreased ability to generate body heat during a fever, so even a low-grade fever can have serious underlying causes in geriatrics.

Abnormal variations

Abnormal patterns include[1]:

  • Hectic "when the difference between peak and trough temperature is great (1.4°C or more)"
  • Sustained when "here is little change (0.3°C or less) in the elevated temperature during a 24-hour period"
  • Remittent is when "the temperature falls each day but not to normal"
  • Intermittent is then the fever is normal at least part of each day
  • Relapsing fever is "a variant of the intermittent pattern, fever spikes are separated by days or weeks of intervening normal temperature"
    • This pattern may occur in "rat-bite fever, malaria, cholangitis, infections with Borrelia recurrentis, Hodgkin's disease (Pel-Ebstein fever), and other neoplasms... Fever at 48-hour intervals suggests Plasmodium vivax or P. ovale; 72-hour intervals suggest P. malariae, while P. falciparum often has an unsynchronized intermittent fever"

Associated symptoms

Arthropathy, when prominent, suggests Parvovirus B19.

Myalgias, when prominent, suggests Dengue fever.

Headache, when prominent, suggests West Nile Virus.

Relative bradycardia

The "pulse rate rises about 15 beats/min for each degree centigrade of fever" Relative bradycardia suggests an intracellular organism such as salmonella, legionella, and chlamydia.[2] Other causes include Sandfly fever, Dengue fever, and maybe some cases of drug induced fever[3].

Psychomotor activity

The distinction between serotonin syndrome, neuroleptic malignant syndrome, malignant hyperthermia, and toxicity from cholinergic agents has been reviewed (see chart).[4] The most difficult distinction is between serotonin syndrome and neuroleptic malignant syndrome as patients may be on drugs that could cause either disorder.

  • Serotonin syndrome shows hyperkinesia, hyperreflexia, and hyperactive bowel sounds
  • Neuroleptic malignant syndrome shows bradykinesia, bradyreflexia and normal or diminished bowel sounds.

A helpful guide is that "dopamine antagonists [such as used to sedate a psychosis] produce bradykinesia, whereas serotonin agonists [such as used to activate a depression] produce hyperkinesia".[4] Lastly, neuroleptic malignant syndrome may develop over several days while serotonin syndrome develops faster.


  1. Dall L, Stanford JF. Fever, Chills, and Night Sweats. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 211. PMID: 21250166.
  2. Babyatsky MW, Keroack MD, Blake MA, Rosenberg ES, Mino-Kenudson M (2007). "Case records of the Massachusetts General Hospital. Case 35-2007. A 30-year-old man with inflammatory bowel disease and recent onset of fever and bloody diarrhea". N Engl J Med. 357 (20): 2068–76. doi:10.1056/NEJMcpc079029. PMID 18003964.
  3. Mackowiak PA, LeMaistre CF (1987). "Drug fever: a critical appraisal of conventional concepts. An analysis of 51 episodes in two Dallas hospitals and 97 episodes reported in the English literature". Ann. Intern. Med. 106 (5): 728–33. PMID 3565971.
  4. 4.0 4.1 Boyer EW, Shannon M (2005). "The serotonin syndrome". N Engl J Med. 352 (11): 1112–20. doi:10.1056/NEJMra041867. PMID 15784664.

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