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 Why measure body temperature?
It is of great medical importance to measure body temperature. The reason is that a number of diseases are accompanied by characteristic changes in body temperature. Likewise, the course of certain diseases can be monitored by measuring body temperature, and the efficiency of a treatment initiated can be evaluated by the physician. Fever is a reaction to disease-specific stimuli, where the setpoint of the temperature control centre is varied to promote the body's defences against the disease process. Fever is the most common form of pathological (disease-related) elevation on body temperature.
What is important in taking temperature?
Essentially, it is true that the measured body temperature always depends on where it is measured. Therefore, contrary to popular consensus, there is no simple "normal temperature.
Furthermore, a healthy person's body temperature will vary with activity and time during the day. In a rectal temperature measurement, a typical temperature difference of 0.5°C between the higher evening temperatures is physiological. Body temperature is typically elevated after physical activity.
Roughly speeking, a distinction is made between a core temperature and a surface, where the surface temperature is measured at the skin surface and is a mixed temperature between the body's core temperature and the ambient temperature. The core temperature is measured by inserting a thermometer into a body cavity, which yields the temperature of the mucous tissue.
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Where should I take the temperature?
The most reliable core temperature is obtained by inserting a thermometer into the rectum (rectal measurement). This measurement is accurate and has low scattering in the results. The normal range is approximately: 36.2°C - 37.7°C.
In women, vaginal temperature measurement yields a slight underestimate of temperature by an average of 0.1°C to 0.3°C in comparison with a rectal measurement with comparable stability.
The oral measurement can be performed as buccal measurement (in the cheek) or as a sublingual measurement (under the tongue). Both measurements underestimate the rectal temperature by approximately 0.3°C - 0.8° C, with the sublingual measurement being preferable to the buccal.
Body surface temperature measurements used clinically in practice are in the arm pit (axillary measurement) and in the groin. In both cases the respective limb is pressed against the body in order to reduce any ambient temperature influence. However, this is successful only to a limited extent with the disadvantage that the measurement time is long. In adults, the axillary measurement is lower than the rectal by approximately 0.5°C to 1.5°C! In infants, these underestimates in comparison with the rectal temperature are much smaller.
Ear thermometers measure the temperature of the eardrum with an infrared sensor. The tip of the thermometer is simply positioned in the ear channel and results are obtained in one second! Next to its convenience this method is very reliable if accuracy can be proven by a clinical validation. Well designed ear thermometers perform very accurately without great scattering in results. An optimised tip shape is the basis for reliable data obtained with infants and babies.
Forehead thermometers offer the least intrusive and therefore most comfortable way to measure body temperature. Simply place the thermometer onto the patient's forehead and an infrared sensor detects the peak reading, while a second sensor measures the ambient temperature. The difference in these readings is analysed, and according to clinically established offsets, a body temperature reading is determined and displayed on the LCD.
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How accurately can I take a temperature?
Essentially a distinction must be made between the technical accuracy of the thermometer itself and the clinical accuracy in use in taking a temperature. The former is determined under idealized conditions to guarantee the quality of the instrument, taking the relevant technical standards into account. An accuracy of +/- 0.1°C can be considered state of the art for high-grade thermometers. The user must not confuse technical accuracy with this accuracy in use. The human body temperatures described here, which depend on the measurement location and time, are due to physiological causes and are not due to a thermometer malfunction. By correctly applying a thermometer, the accuracy can be strongly increased (follow the operating instructions!)
Some thermometry data:
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Where used:
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Normal range
typical lower
limit T/(°C)
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Normal range
typical upper
limit T/(°C)
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Contact thermometer
Max. value mode
Typ. measurement time tm/(sec)
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Rectum
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36.2
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37.7
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10-60
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Vagina
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36.0
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37.5
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-
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Orally (buccally)
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35.5
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37.1
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30-60
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Orally (sublingually)
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35.7
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37.3
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30-60
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Axillary
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35.2
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36.7
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30-60
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Ear
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35.8
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37.1
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1
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Forehead
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-*
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-*
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1
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