By Manuel M. Ruiz, May 23, 2020
Today is World Metrology Day. Happy World Metrology Day despite the inconveniences we are experiencing due to the quarantine and lockdown brought about by the COVID-19 pandemic.
One common sight nowadays is the use of Infrared Thermometers, IRTs to screen for fever, the most detectable and probable symptom of COVID-19 infection. But how accurate are these IRTs? Are they calibrated?
Metrology has been put on the spot with these questions and the only way to give an honest answer is to perform a calibration on them - a metrology function.
Performing a calibration on these IRTs at this time however is virtually impossible to accommodate due to their sheer number all waiting to be done at the same time. There is also the inconvenience of pulling them out of service for calibration at a time when they are most badly needed.
This was the same debacle the National Institute of Metrology, China (NIM China) went through when it experienced the sudden surge of demand for the calibration of their IRTs at the onset of the epidemic. Because of the emergency situation, NIM China proposed and used a stop-gap DIY method of checking the accuracy of the IRTs instead of the usual but more rigorous calibration process performed in the laboratory. This consisted of comparing the readings of an IRT with a known working and accurate thermometer, for example, a digital or liquid-in-glass thermometer.
A similar method is now being proposed here in the Philippines as another contribution of metrology in the fight against the COVID-19 pandemic. The method just relies on the IRT’s ability to distinguish between normal temperature from an elevated temperature. This method involves measuring and noting down the temperature of a normal healthy human subject (individual) using the IRT and then in turn measuring the temperature of the person being screened using the same IRT.
An elevated temperature, a temperature appreciably above the temperature of a healthy individual would be enough reason for further screening by other means (like using a digital or liquid-in-glass thermometer). In this case, we are not trying to measure the absolute temperature (which requires honest to goodness calibration) but just interested in the presence of an elevated temperature.
For example, an IRT measures the temperature of a healthy individual to be 34 °C. If the same IRT measures an elevated temperature of say 36 °C on an individual under screening, that would be enough reason to suspect the presence of fever in that person. What we want to determine simply is an elevation of 2 °C above the temperature of a normal healthy individual could be a sign of fever.
We are hoping that with this simple and easy to perform procedure, our COVID-19 front liners are better equipped to screen for elevated temperature which is a sign of probable COVID-19 infection (without having their IRTs actually calibrated).