Ear thermometers 'unreliable'

Back to basics: Mercury thermometer

Ear thermometers - used widely in homes and hospitals - are not accurate enough to be totally reliable, say researchers.

It is claimed that they could miss a fever in a child ,and could be unreliable in many hospital settings in which precision is required.

A rectal temperature test with a traditional thermometer is far more accurate, they say.

Ear thermometers work by picking up infrared emissions from tissue inside the ear, and using them to calculate internal body temperature using this.

They are a godsend to many stressed parents who are unwilling to administer a rectal thermometer test, and find their child is too restless to hold a mercury thermometer under the tongue for minutes at a time.

This finding means that the presence of fever might not be detected

Liverpool University Institute of Child Health researchers

Many doctors have started using them regularly for the same reasons of convenience.

However, research published in The Lancet warns against relying on them too heavily.

There have been many individual studies of the accuracy of ear thermometers - with varying results, and scientists from the University of Liverpool Institute of Child Health pooled them to come up with an overall conclusion.

Illusion

Rectal temperature has long been considered the most accurate representation of core temperature.

When the results of ear thermometry were compared with rectal tests, significant disparities emerged.

For example, if a rectal temperature was 38C, ear temperature could vary from just over 37C up to more than 39C.

This could give the illusion of normality when in fact a temperature was slightly raised - or portray a patient to be more feverish than he or she actually was.

Even when the infrared device was used rectally, it did not give a particularly accurate reading.

Vulnerable

In a hospital setting, it is particularly important to know the accurate temperature of young babies and people who have weakened immune systems, as slight differences in temperature can mean significant differences in a patient's condition.

The researchers wrote: "The implications of our findings are that measurements taken with infrared ear thermometry cannot be used as an approximation of rectal temperature, even when the device is used in rectal mode.

"This finding means that the presence of fever might not be detected, and accurate temperature might not be obtained in situations in which body temperature needs to be measured with precision."