Laboratory evaluation of forehead infrared radiation thermometers (FIRTs) used for core body temperature measurements

Purpose The main objective of this work was to evaluate, in laboratory, the reliability of temperature measurements performed by forehead infrared radiation thermometers (FIRTs), widely employed for body temperature measurements as a policy for preventing the spread of Covid-19. Additionally, the suitability of commercial infrared thermometer calibrators for the characterization of those FIRTs was assessed. Methods Eighteen FIRTs of ten different models available in the Brazilian market were calibrated employing a commercial flat-plate infrared thermometer calibrator and a custom-designed blackbody cavity as reference thermal radiation sources. The thermometers were assessed with respect to their accuracy and reproducibility, under laboratory conditions, according to the ISO/IEC 8061–2-56:2017 standard. The FIRTs were calibrated both in direct (uncorrected) and adjusted (corrected for estimating the temperature in a specific body site) modes. Results The results showed that only 50% of the FIRTs evaluated were approved in the laboratory accuracy tests, performed in direct mode. In adjusted mode, the agreement of the measurements performed by different models was very poor when compared with each other. The results also showed good agreement between the calibration results performed by the blackbody cavity and the commercial infrared calibrator, despite the high uncertainties obtained with the latter. Conclusion The results found show that the FIRTs available in the market are not, in general, reliable instruments for detecting febrile individuals. This conclusion is based on the poor agreement of the measurement results obtained with different FIRT models in adjusted mode, even though some models have shown good performance when assessed in direct mode, under laboratory conditions. In the absence of a skin temperature standard, clinical tests with real people are necessary to confirm the results found in this study. The results also show that even though there is good agreement between the measurements performed with the calibrator and the blackbody cavity, the uncertainties of the measurements performed with the calibrator are still too high to support the use of these devices for testing FIRTs with sufficient accuracy.