Proper use of
thermometers to
measure body
temperature
Medical Device Division
E-mail : mdd@dh.gov.hk
Website : www.mdd.gov.hk
General Guidelines on measuring
body temperature and using
thermometer
1. Compare the accuracy, suitability,
convenience and price of thermometers
before purchase.
2. Choose a thermometer and method of
measurement which suit the individual‘s
age and health condition; Consult
healthcare professionals if in doubt.
3. Patients with communicable diseases
should use personal thermometers to
avoid cross-infection.
4. Familiarise with the correct use of
thermometer and temperature reading
by referring to the user instructions
provided by manufacturer.
5. Avoid activities that would distort
temperature measurement (e.g.
drinking hot water immediately before
taking oral temperature).
6. Clean and maintain the thermometer
according to the procedures
recommended by the user instructions.
7. In case body temperature needs to be
taken regularly, take the temperature at
the same time of each day and use the
same temperature taking method to
allow comparison.
8. If there is any doubt about the body
temperature reading, please consult
healthcare professionals.
Types of thermometer and
specific precautions
Description Special points to note*
Mercury-in-glass/ Alcohol-in-glass Thermometer
Measures oral,
rectal or armpit
body temperature
through the
thermal
expansion of
mercury/ ethanol
As mercury spill is hazardous to
environment and health, the use of
mercury thermometer should be
avoided as far as possible.
Thermometer should be reset by
shaking the mercury/ ethanol level
down below 35°C (95°F) each time
before using.
The tips of oral thermometer and
rectal thermometer are different in
shape (slender vs. round) and must
not be cross-used.
Electronic (digital) Thermometer
Measures oral,
rectal or armpit
body temperature
by means of
thermistor with its
resistance varying
according to the
temperature
Temperature difference among oral,
rectal and armpit body temperature
should be noted.
Infrared Thermometer
Measures thermal
radiation
(infrared) emitted
from ear and
forehead to infer
body temperature
For ear thermometer, a new ear-probe
jacket should be used for different
person; the ear canal must be pulled
straight when measuring.
Forehead thermometer should only be
used for screening instead of
diagnostic purpose due to greater
measurement error.
Oral
Rectal
* Users should read and follow the instructions in the user
manual of the thermometer because operation procedures
may vary among brands
www.mdd.gov.hk
Thermometer can be
used to check the body
temperature to see
whether a person has a
fever. This pamphlet
provides an introduction
to body temperature, its
measurement methods
and proper use of various
types of thermometer.
There are two ways to measure body temperature —
by measuring core temperature and surface
temperature.
Body Temperature
Body
temperature
measurement
Meaning
Measurement
taken through
Core
temperature
Temperature of
deep tissues
Oral cavity, ear
canal, rectum
Surface
temperature
Temperature of
surface skin
tissues
Forehead, armpit
Since surface temperature is more susceptible to
changes in the surroundings, it is considered less
accurate and is recommended for use only when
there is difficulty in measuring the core temperature.
Comparison among different measurement methods
Measurement method Oral Ear Rectal Forehead Armpit
Suitability
Infants and children below 6
Cooperative
Adults and
children
above 6
Uncooperative
Unconscious
Accuracy
☺☺☺ ☺☺☺ ☺☺☺ ☺ ☺☺
Convenience and speed
☺☺☺ ☺☺☺ ☺ ☺☺☺☺ ☺☺
Reference level for fever
> 37.5°C
(99.5°F)
> 38°C
(100.4°F)
> 38°C
(100.4°F)
> 36°C
#
(96.8°F)
> 37.3°C
(99.1°F)
Measurement methods and specific precautions
Measurement method Unsuitable conditions for the measurement method
Oral
● Suffering from shortness of breath
● Sneezing repeatedly, having a hard cough or suffering a seizure
● Unconscious or confused
● Unable to close the mouth tightly
Ear
● Having a middle ear infection
● Obstruction of ear canal by ear wax
● Wearing hearing aid
Rectal
● Large amount of faeces accumulated in the rectum
● Rectal diseases, e.g. haemorrhoid or diarrhoea, etc.
● Just undergone intestinal operation
● Having wounds/ lesions in the anus
Armpit
● Unable to secure thermometer under the axilla
Forehead
● Forehead being covered (e.g. by bandage/ cooling gel sheet)
Infrared forehead
thermometer
Infrared ear
thermometer
3
# >36°C is only a reference level which may vary from brands and models of infrared forehead thermometers.
Users should refer to the user manual of the thermometer or check with the manufacturer / supplier.
