3.1 - Body Temperature

Meaning and Importance of Body Temperature

• Temperature is the degree of hotness or coldness of a substance.
• Body temperature is the degree of hotness or coldness of the human body.
• Body temperature must remain within the normal range so that the body can function at its optimum level.
• An increase or decrease in body temperature indicates a possible health problem.
• Body temperature is measured using a thermometer.

Types of Thermometers

Type	Use and measuring range
Clinical thermometer	Measures body temperature; range: 35°C to 42°C
Laboratory thermometer	Measures the temperature of liquids; range: −10°C to 110°C
Rectal thermometer	Measures body temperature through the rectum
Infrared thermometer	Measures body temperature without contact with the body

Correct Techniques for Measuring Body Temperature

Clinical thermometer

1. Ensure that the thermometer reading is below 35°C before use.
2. If it exceeds 35°C, shake the thermometer until the reading falls below 35°C.
3. Place it under the armpit or in the mouth for approximately 2–3 minutes. For a digital clinical thermometer, wait until a beep is heard.
4. Remove the thermometer and record the temperature.

• The constriction prevents the mercury from falling quickly after the thermometer is removed from the mouth or armpit, allowing a more accurate reading.
• A clinical thermometer measures temperature to an accuracy of 0.1°C.

Laboratory thermometer

• It is unsuitable for measuring body temperature because it has no constriction in its mercury column.
• When removed from the mouth or armpit, its reading falls quickly and may become inaccurate.
• If it is used to measure body temperature, take the reading while it is still in the mouth or under the armpit.
• A laboratory thermometer measures temperature to an accuracy of 1°C.

Clinical thermometer	Laboratory thermometer
Has a constriction	Has no constriction
Reading can be taken after removal from the body	Reading must be taken while the thermometer is still in position
Accuracy: 0.1°C	Accuracy: 1°C

Rectal thermometer

1. Use a thermometer labelled for rectal use; it is normally used for infants below 3 months old.
2. Clean the thermometer tip with alcohol.
3. Apply petroleum jelly to the tip.
4. Lift the infant’s legs.
5. Insert the thermometer approximately 1.5–2.5 cm into the rectum.
6. Leave it in place until a beep is heard.
7. Record the temperature.

Infrared thermometer

1. Use the thermometer without touching the individual.
2. Point it at the individual from a distance of approximately 5 cm.
3. Do not point it directly or indirectly towards the eyes.
4. Record the temperature; the reading is obtained very quickly.

Interpreting Body Temperature

• Normal human body temperature is 36.9°C.
• A temperature above 37°C may indicate a fever.
• Factors that can raise body temperature above normal:
  • infection by bacteria or viruses;
  • exposure to extreme heat, such as heatstroke or extreme sunburn;
  • exercise, especially vigorous exercise.
• Exposure to extreme cold can lower body temperature below normal and may be fatal.