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Covid response

Temperature measurement

Guidance on fever screening

NPL is an expert on measuring body temperature and helped develop the standards for fever screening and clinical body temperature measurements. It also contributed to an FDA study on the use of thermal imaging for fever screening in 2018. During the COVID-19 pandemic NPL was approached by government bodies, councils, hospitals, transport organisations and measurement companies, for advice and guidance on accurate temperature measurements, the available technology and its fitness for purpose.

Temperature measurements during the COVID-19 pandemic was primarily done using digital electronic thermometers, which are known to have an uncertainty in the reading from 0.5 to 1 °C. NPL contributed evidence to the Department of Health and the Chief Scientific advisers on clinical temperature measurement. Early guidelines on detecting COVID-19 stated that a temperature of 37.8 °C was a critical, but this was changed to using touch to detect for elevated temperatures. This was particularly important for elderly patients who often have a fever without reaching a threshold ‘fever’ temperature, and also reflected the accuracy to which a temperature can measured.

Fever screening has been deployed in certain situations over the past few years but was not regarded as a useful tool for COVID-19 detection, since approximately 80% of carriers are asymptomatic and 10% do not exhibit a fever. NPL advised that many thermal imaging systems that had been considered or deployed did not comply with the standards, did not give traceable measurements and many cases were not clinical instruments, so had high measurement uncertainties associated with the data they generated.

Authoritative advice

NPL gave advice to organisations testing or screening patients in hospitals and care homes, who wanted to have higher confidence, with lower uncertainty, although widespread fever screening was not recommended for COVID-19. NPL also advised on suitability of using thermal imaging for fever screening.   

NPL’s role through the COVID-19 pandemic was to advise on the deployment of reliable fever screening systems and provide confidence in temperature measurements. As the National Metrology Institute and a leading expert in the area, NPL disseminated the current guidelines and information. NPL are now leading a new Consultative Committee on Thermometry for clinical applications, a working group made up from experts from NMIs internationally. In future pandemics, temperature measurement may be used as a key indicator, and the technology and procedures need to be in place to support it.

Impact during COVID-19

  • Disseminating authoritative advice that people can trust and rely on
  • Highlighting the critical issues round temperature measurements in humans and the lack of information in some areas
  • Ensuring advice on temperature measurement and fever screening is data driven

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