The impact of the different human body parts on temperature measurement

• Rectal measurement

Taking a rectal measurement is the most reliable way to obtain a core temperature value.  Result variation with this type of measurement is low and the precision is particularly high.  The normal temperature range is approximately between 36.6°C and 38.0°C.

• Oral measurement

An oral measurement can be taken as a buccal measurement (in the cheek) or as a sublingual measurement (under the tongue).  In both cases, the temperature measured is below the measured value of a rectal measurement - approximately up to 1.1 °C.  Whereby a under the tongue is preferable to a in the cheek measurement.  The normal oral temperature range is approximately between 35.5°C and 37.5°C.

• Axillary measurement

Measuring the body’s surface temperature is normally conducted by medical staff in the armpit (axillary measurement) and in the groin.  The respective limb is pressed against the body to reduce the possible influence of the ambient temperature.  However, this is only possible up to a certain body mass and this type of measurement also takes a long time.  In adult patients, the temperature of an axillary measurement is lower than a rectal measurement - up to 1.9°C.  The normal axillary temperature range is approximately between 34.7°C and 37.3°C.

Choose the right type of thermometer

There are different thermometers to choose from, depending on which body area you wish to take measurements from.

• Ear thermometer

The temperature of the eardrum is measured with an infrared sensor.  The tip of the thermometer is simply inserted into the ear canal and the measurement result is available quickly.  In addition to the ease of use, this measurement method is also very reliable.  Carefully constructed ear thermometers measure with a very high degree of accuracy and have low result variation.  An optimally shaped thermometer tip is a prerequisite for precise measurements in infants and children.  The normal ear temperature range is approximately between 35.5°C and 37.7°C.

• Forehead thermometer

These are perceived as the least disruptive and therefore the most comfortable way to measure body temperature.  The forehead thermometer is placed on the forehead of the patient.  An infrared sensor detects the highest measured value, while a second sensor measures the ambient temperature.  The difference between these two measured values, taking into account clinical equalisation calculations, gives the body temperature which is shown on the LCD display.  The normal temperature range on the forehead is approximately between 35.4°C and 37.4°C.

• Digital thermometer

Digital thermometers are the most accurate and quickest form of thermometer.  The readings are obtained from the underside of the tongue, the rectum, or the armpit.  They are widely available in local pharmacies and can be utilised at home or in hospitals.  They’re small and portable, and it is simple to read the display.  A digital thermometer is reasonably priced.  They do not need any particular care.

The accuracy of the temperature measurement

It is important to differentiate between the technical accuracy with which the thermometer takes a reading and the clinical reliability of the specific measuring method.  The accuracy of the thermometer is determined under ideal conditions in accordance with the relevant technical norms, in order to guarantee the measuring instrument’s quality.  Modern high quality thermometers measure with an accuracy of +/-0.1°C.

The technical precision and clinical reliability in the use of the thermometer should not be confused.  Human body temperature varies depending on where on the body the temperature is taken and the time of measurement.  This is due to physiological factors and must be distinguished from thermometer malfunction.  Measurement accuracy primarily depends on whether the thermometer is used correctly (read the operating instructions!).