How Accurate Are IR Thermometers?

When trying to measure fever temperatures

On the news we see lots of images of people pointing a compact Infrared (IR) Thermometer a person’s forehead to determine if they have a fever or not. In many cases if done as a really coarse screening tool, it’s probable adequate.

Well, the question naturally arises: How “Accurate*“ is the measurement?

Without knowing the specific IR Thermometer in use, it is possible to create a practical estimate based on both typical industry product specs and on the detailed research done by one of the leaders in the field of noncontact Infrared Temperature measurement of humans, the Exergen Corporation.

Why Exergen? It’s simple. 

They are one of the most technical and prolific developers of no-touch, IR Thermometers in the world, ones developed specifically for the measurement of human body temperature.

They call their devices “Temporal Artery Thermometers” because their extensive research has shown this to be an excellent and highly reproducible method of measurement.

“Clinical accuracy per ASTM E1112“ is +/- 0.1 Deg. C given for the Exergen Model TAT-5000 on the Exergen website.

Most IR Thermometers developed for general use, not specifically intended for measuring human body temperature, usually have a relatively wide measurement range, like 0 to 500 Deg. C. Typical calibration specification is +/- 1 Deg. C or 2% of reading, whichever is greater.

The best “Accuracy” one should expect in use at around 37 Deg. C is then +/- 1 Deg. C, but the errors in use at least double that. So one should not be surprised that both false positives and false negatives will likely occur at a specific measurement target temperature, like 37.5 Deg. C.

There is some useful information on the FDA website at: https://www.fda.gov/medical-devices/general-hospital-devices-and-supplies/non-contact-infrared-thermometers.

Ear Thermometers were introduced more than 20 years ago and have a mixed response from their users. They need careful use and can produce false negatives for fever measurement if not done correctly.

The following webpage from the Mayo Clinic compares the several methods of body temperature: https://www.mayoclinic.org/diseases-conditions/fever/in-depth/thermometers/art-20046737.

Below are links to some additional resources on human body temperature measurement.

E825-98(2016) Standard Specification for Phase Change-Type Disposable Fever Thermometer for Intermittent Determination of Human Temperature

E1061-01(2014) Standard Specification for Direct-Reading Liquid Crystal Forehead Thermometers

E1104-98(2016) Standard Specification for Clinical Thermometer Probe Covers and Sheaths

E1112-00(2018) Standard Specification for Electronic Thermometer for Intermittent Determination of Patient Temperature

E1299-96(2016) Standard Specification for Reusable Phase-Change-Type Fever Thermometer for Intermittent Determination of Human Temperature

E1965-98(2016) Standard Specification for Infrared Thermometers for Intermittent Determination of Patient Temperature

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* Accuracy is the misnomer that many instrument makers put in their literature but it is not a quantitative technical term recognized by those who study and understand measurement science (metrology). It is a qualitative term much like “beauty” and “colorful” are. People believe that it describes how well a measurement devices measures, yet, it does not. The more precise term, used by Metrologists is “Measurement Uncertainty“ and, when used to fully describe a measurement result quantitatively, it includes a Confidence Level and limits. See the page on this site for more details https://grpeacock.blogspot.com/p/uncertainty.html.