Q & A about Fever Monitoring
- How accurately can I take a temperature?
- Where should I take the temperature?
- What is important in taking a temperature?
- Why measure body temperature?
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 idealised 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!)
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 approx. 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 a buccal measurement (in the cheek) or as a sublingual measurement (under the tongue). Both measurement underestimate the rectal temperature by approx. 0.3°C to 0.8°C, with the sublingual measurement being preferable to the buccal.
The only types of body surface temperature measurement used clinically in practice are the arm pit (axially measurement) and in the groin (inguinal measurement). 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 approx. 0.5°C to 1.5°C!
In infants, these underestimates in comparison with the rectal temperature are much smaller.
Contactless thermometers measure the radiant heat emitted by heat source. The surface temperature can be deduced from this radiation. Today manly ear thermometers are in use. They aim to quickly measure the temperature of the ear drum.
What is important in taking a temperature?
Essential, it is true the measured body temperature always depends on where it is measured. Therefore, contrary to the 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 temperature and the lower morning temperature is physiological. Body temperature is typically elevated after physical activity.
Roughly speaking, a distinction is made between a core temperature and a surface temperature, 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.
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 disease 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 defense against the disease process. Fever is the most common form of pathological (disease-related) elevation of body temperature.