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Temperature can be measured by many methods. These include the following thermometers:

  • mercury thermometer

  • digital electronic pacifier

  • digital peak hold LED thermometer

  • digital infrared aural

  • electronic probe

  • forehead thermometer (temporal area).

The favoured general instruments for oral and rectal use are the digital peak hold and mercury thermometers, although the mercury type is now less popular and not favoured for infant use by the American Academy of Pediatricians.

Table 18.1 gives a basic guide to interpreting the temperature values obtained.

Table 18.1

Interpretation of temperature measurement

The mercury thermometer

Basic rules of usage

  1. Before use, shake down to 35–36°C.

  2. After use:

    • shake down and store in antiseptic

    • do not run under hot water

    • wipe rectal thermometers with alcohol and store separately.

  3. Recording time is 3 minutes orally, 1 to 2 minutes rectally.

Oral use

  1. Place under the tongue at the junction of the base of the tongue and the floor of the mouth to one side of the frenulum—the ‘heat pocket’.

  2. Ensure that the mouth is kept shut.

  3. Remove dentures.

Note: Unsuitable for children 4 years and under, especially if irritable.

Rectal use

A suitable route for babies and young children under the age of 4.1


  1. Lubricate the stub with petroleum jelly.

  2. Insert for 2–3 cm (1 inch).

  3. Keep the thermometer between the flexed fingers with the hand resting on the buttocks (Fig. 18.1).

Fig. 18.1

Rectal temperature measurement


  • Dig thermometer in too hard.

  • Hold it too rigidly.

  • Allow the child to move around.

Axillary use

Although unreliable, it is practical for young children and gives a helpful guide. If used it should be placed high in the axilla for 3 minutes.1

Groin use

This route is not ideal but is more reliable than the axilla. It closely approximates oral temperature.

In infants, the thigh should be flexed against the abdomen.

Vaginal use

Mainly used as an adjunct to the assessment of ovulation during the menstrual cycle. Should be placed deeply in the vagina for 5 minutes before leaving the bed in the morning.

Digital peak hold thermometer

This ...

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