Infrared thermometry is a non-invasive tool to assess body temperature which uses an infra-red thermometer instead of the mercury in glass forms. This modality is capable of detecting infrared radiation from inside the ear canal (some relate this to the tympanic membrane) that is then equated to the temperature of the body. The information can be used clinically as part of the assessment of a patients vital signs.

In 2001, we initiated a collaboration to study these devices due to the poor reputation and loss of confidence in them by the medical profession. This collaboration included members of the scientific, medical and nursing communities. A PhD project (funded by the National Physical Laboratories) considered the issue of traceability and on site calibration of the devices whereas the use and training was the remit of the nursing group. We (along with other clinical collaborators) considered the elements of physiological variability and reliability of temperature measurement in a variety of populations.

General findings to date

The IR thermometer has a good reliability but should be regularly checked against a traceable standard.

The methodology should be standardised and taught to all users by an individual who is fully conversant with the device and its possible pitfalls.

There should be an appreciation of the variations found in the healthy / asymptomatic population.

The relationship between temperature measurements from different sites has not been fully elucidated in symptomatic subjects and should not be extrapolated from work performed on healthy / asymptomatic subjects.

In built “corrections” to give a rectal equivalent temperature are not robust.

Temperature should be assessed in both ears, as occasional differences of up to 2°C may be found. If no infection is present in the ear canal, the highest temperature would be most likely to be representative of the subjects body temperature.

The perception of these thermometers being unreliable probably originates from the ability they have to give temperatures within a small period of monitoring (seconds). This created the opportunity to make measurements in rapid succession for the first time, giving the potential to reveal small physiological variations in temperature at the site being monitored. This, coupled with the normal variation of the sensor (at best ±0.1°C), leads to fluctuations which can cause insecurity in those users who are not scientifically trained.

Current work

Study of radiometry of the scalp and its relationship to aural temperature.
Relationship between age, sex and somatotype and bilateral differences in ear temperature.

Correlation of temperature measured at the seat surface interface with comfort.

Heusch AI. Suresh V. McCarthy PW. The effect of factors such as handedness, sex and age on body temperature measured by an infrared 'tympanic’ thermometer. Journal of Medical Engineering & Technology. 30(4):235-41, 2006

Heusch AI. McCarthy PW. The patient: a novel source of error in clinical temperature measurement using infrared aural thermometry. Journal of Alternative & Complementary Medicine. 11(3):473-6, 2005

McCarthy PW. Heusch AI. The vagaries of ear temperature assessment. Journal of Medical Engineering & Technology. 30(4):242-51, 2006 Jul-Aug.

McCarthy PW. Heusch AI. Diagnostic device: an authentic stimulation device and objective assessment tool for detecting presence of vibration related neurovascular conditions of the hand and arm. 2006 BRITISH PATENT FILING No. 0516067.
EUROPEAN PATENT Publication no. EP1749588:

McCarthy PW. An authentic stimulation device for quantifying a person’s reaction to vibration. Advances Wales 2008

Williams M, Heusch AI & McCarthy PW. Facial temperature correlation with ear temperature. Physiological Measurement (2008) Mar;29(3):341-8. Epub 2008 Feb 22

McCarthy PW.. Heusch, AI. Kenkre, J. Machin, G. Suresh, J. Infrared ear thermometers versus rectal thermometers. Comment on: Lancet. 2002 Aug 24;360(9333):603-9; Lancet. 360(9348):1882-3, 2002 Dec 7.