A5V4d

4 Thermometers and the
detection of fever
Introduction
Body temperature in children can be measured at a number of anatomical sites using a range of
different types of thermometers. Sites used to measure temperature include the mouth, rectum and
axilla. The types of thermometers available include mercury-in-glass, electronic, chemical and
infrared. Mercury-in-glass thermometers were the traditional type of thermometer used to measure
body temperature but they are no longer recommended for use in infants and young children because
of the risks of breakage and mercury spillage. 27 Furthermore, UK health and safety regulations require
that mercury-containing medical devices should not be used whenever a suitable alternative exists. 28
Mercury-in-glass thermometers will not be considered further in this guideline except as a comparator
in diagnostic studies.
Electronic thermometers are widely used by healthcare professionals as an alternative to mercury-inglass
thermometers. Electronic thermometers have the advantages of being accurate and very quick
to use but they are often complex and quite expensive pieces of medical equipment. Recently,
cheaper compact electronic thermometers have been produced and these are available for use by the
public as well as healthcare professionals. Chemical phase-change thermometers measure body
temperature by using a combination of chemicals that change colour in response to variations in
temperature. These can either be chemical dot thermometers where the chemicals are contained in
cells on a plastic stick, or chemical forehead thermometers which consist of a patch of chemicals in a
plastic pouch that is placed on the forehead. Chemical dot thermometers are usually designed for
single use but reusable types are available. All types of chemical thermometers can be used by the
public. In recent years, infrared thermometers have been used more and more frequently. This type of
thermometer detects infrared radiation from blood vessels and this is then used to estimate central
body temperature. Most thermometers of this type measure temperature at the eardrum (infrared
tympanic thermometers) but temporal artery thermometers are now available where temperature is
measured on the scalp. Infrared thermometers are quick, non-invasive and simple to use. They are
relatively expensive, however.
In this chapter, the different sites and thermometers are compared with regard to their accuracy in
measuring true body temperature and their ability to detect fever. In general, the various sites and
different types of thermometers are compared in their diagnostic ability against a traditional gold
standard. The gold standard is usually a measurement with a mercury-in-glass or electronic
thermometer using the mouth in older children and the rectum in young children and infants. This
chapter also looks at the ability of parents and carers to detect fever in young children using
subjective means such as palpation of the child’s brow.
4.1 Thermometers and the site of measurement
Review questions
How accurate are the different types of thermometer in the measurement of body temperature in
young children, and how do they compare in their ability to detect fever?
How accurate are the readings of temperature from different sites of the body in young children, and
how do these sites compare in the ability to detect fever?
Body temperature can be recorded from a number of sites in the body in babies and young children.
Traditionally, temperature was taken by the oral route in older children and adults, while the rectal
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