Fever Measurement and Fever Types

Body temperature is usually measured with a clinical thermometer (= fever measurement). The most accurate measurement is the rectal measurement (gold standard). The rectal reading is closest to the core body temperature, i.e., the temperature of the vital internal organs.The measurement can also be taken orally (mouth), axillary (armpit), or auricular (ear; measurement error possible due to earwax).

Measurement location Measurement duration [minutes] Deviation from rectal measurement [°C]
Rectal 3-5
Oral 5-8 (0,3-0,5) – > 0,5
Axillary 10 > 0,5
Auricular 1-3 seconds > 0,5

Note: All noninvasive central methods (oral, axillary, and auricular fever measurement) did not guarantee a clinically acceptable agreement of ± 0.5 °C. In addition to the conventional clinical thermometer, the following alternatives are available:

  • Digital thermometers
  • Tympanothermometer (ear thermometer)
  • Forehead thermometer
  • Infrared thermometer

The fever is usually measured in the morning between 7 and 8 am (daily temperature minimum) and in the afternoon / evening between 17.00 and 18.00 (-20.00) clock (daily temperature maximum);

Normal fluctuations in core body temperature

Temperature is lowest in the early morning (rectal about 36.5 °C) and has a maximum in the afternoon (rectal 37.8 °C). During sleep, a minimum sets in about 2 am; then, before awakening, the temperature slowly rises again. Fluctuations in temperature depend on many factors such as time of day, meals, emotions, or physical activity (increase to 2 °C depending on activity level). In a study of 35,488 patients who neither had an infection nor were taking an antibiotic, a mean oral temperature of 36.6 °C (95 percent confidence interval 35.7-37.3 °C; 99 percent confidence interval 35.3-37.7 °C) was measured. Measurements at different regions (versus oral): temporal: -0.03 °C; tympanic: -0.06 °C; axillary: -0.26 °C. Several comorbidities (concomitant diseases) were associated with lower temperatures (e.g., hypothyroidism: -0.013 °C, P = 0.01) or higher temperatures (e.g., cancer: 0.020 °C, P < 0.001).Normal body temperature also varies with age (infants have a temperature approximately 0.5 °C higher than children and adults). In women, temperature also varies by approximately 0.5 °C over the monthly cycle (increase in basal body temperature). The mean orally measured temperature is 36.8 °C.The mean rectally measured temperature is 37.2 °C.

Fever

Fever 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 a nonspecific symptom that indicates the presence of a disease but does not provide information about its character or cause and localization. The increase in temperature during illness serves to accelerate endogenous metabolic processes and thus promotes the body’s immune responses. Fever is accompanied, among other things, by an increase in pulse rate (ten heartbeats per minute more per 1 °C increase in body temperature, so-called “Liebermeister rule”) (exception: typhoid abdominalis: bradycardia (heartbeat too slow: < 60 beats per minute)). Note: In elderly patients, a rectally measured body temperature greater than 37.8 °C may indicate a bacterial infection!

Definition of fever

Fever is defined as a rise in rectal temperature to 38°C and above.

Description °C
Subfebrile temperature -38 °C
Mild fever 38.1 °C – 38.5 °C
Moderate fever -39 °C
High fever 39.1 °C – 39.9 °C
Very high fever > 40,0 °C

Fever types

Fever type Description Typical diseases
Febris continua(continuous fever; continua fever).
  • Fever is circa 39 °C and fluctuates by up to 1 °C during the day
  • It lasts for several days
Spotted fever, lobar pneumonia, rickettsioses, typhoid fever, paratyphoid fever, scarlet fever, tularemia.
Febris remittens(remittent fever).
  • Fever fluctuates by 1-2 °C during the day, but also permanently exceeds normal temperature
Tuberculosis
Febris intermittens(intermittent fever)
  • Peaks of fever with chills alternate with normal and also low temperature, temperature fluctuates by several °C daily
Acute brucellosis, endocarditis, malaria, miliary tuberculosis, osteomyelitis, salmonellosis, sepsis.
Relapsing fever(recurrent fever, recurrent fever).
  • Short periods of fever are interrupted by fever-free days
Malaria (marsh fever, alternating fever), relapsing fever,
Febris undulans(undulating fever; undulating fever; also called Pel-Ebstein fever).
  • The fever progresses in waves with fever peaks up to 40 °C
Brucellosis, Hodgkin’s lymphoma (synonyms: Hodgkin’s disease, lymphogranulomatosis).
Double-giped fever
  • After a few fever-free days, a second febrile phase occurs after an initial fever peak
Dengue fever, yellow fever, influenza (including pandemic/avian influenza or “new flu“/” swine flu“), measles.

When does a child with a fever need to see a doctor?

Babies with fever generally belong to the pediatrician and adolescent doctor. Older children should be presented to him in the following cases:

  • The fever rises above 38.5 °C.
  • The fever persists for more than three days.
  • The child refuses to drink, loses fluid and becomes dehydrated.
  • The child is well, but vomiting lasts longer than twelve hours (if the child is not well, earlier to the doctor!).
  • The child is well, but diarrhea lasts longer than two days (if the child is not well, earlier to the doctor!).
  • The child has severe abdominal pain or cramps.
  • The pain is getting worse despite treatment.
  • The child convulses.
  • The child has a skin rash or shows symptoms of ear pain or breathing difficulties.