Accuracy of strip-like forehead thermometers

March 18, 2020

Jon Brassey, Carl Heneghan

Oxford COVID-19 Evidence Service Team
Centre for Evidence-Based Medicine, Nuffield Department of Primary Care Health Sciences
University of Oxford

Lay Summary by Mandy Payne, Health Watch

Verdict: If peripheral thermometers are used they will not detect a fever in about 4 in every 10 children with one.  Peripheral thermometers should not be relied on by clinicians to influence clinical decision making. If there is no alternative, consider the actual temperature measurement will be at out by at least +/-1.5°C and ask for repeated measurements.

Young Children

In young children the advice is straightforward and is found in NICE’s recent guideline on in the under 5s where they state:

“1.1.5 Forehead chemical thermometers are unreliable and should not be used by healthcare professionals.”

Children

For children generally (as opposed to just the under 5s) the evidence appears variable! The earliest paper we found was “An Evaluation of a Plastic Strip Thermometer” which reports “We conclude that the Clinitemp is unacceptable as a substitute for the mercury/glass thermometer.” In the same year, a smaller study (n=134) reported: “Parents who rely on these strips to identify a fever in their children may be misled by an erroneous afebrile reading.”

A 1996 study with 120 patients (20 in each of six age groups: < 1 month, 1 to 5 months, 6 to 11 months, 12 to 23 months, 2 to 14 years, and adults concluded: that previous studies have all used inappropriate methods of analysis….. Forehead strip thermometers are easy to use, but they do not estimate the rectal Temperature as accurately as the axillary Temperature does.”

A more recent cross-sectional  2018 study of 995 children found that temporal measurement of temperature is not recommendable, but the ear measurement proved useful for screening purposes, especially among children aged six months to 5 years.

Children and Adults

Three reviews were found with the earliest being the 2010 RACGP review which concluded:

“The digital thermometer provides the best agreement with the mercury in glass thermometer. The infrared tympanic thermometer may be a preferable option for the uncooperative patient. The liquid crystal forehead thermometer is best used at home.”

In 2012, Healthcare Improvement Scotland produced a technology scoping report that found:

• Evidence from a range of adult and paediatric patient groups suggests that temporal artery thermometers are insufficiently accurate for clinical use in inpatient settings

Six studies compared both temporal artery thermometers (TAT) and infrared in-ear thermometers four studies favoured TAT.

infrared in-ear thermometers

A 2015  systematic review of  75 studies (n = 8682) on the accuracy of Peripheral Thermometers for Estimating Temperature reported that most studies at high or unclear risk of bias. The main results were:

• Peripheral thermometers had pooled 95% limits of agreement outside the predefined clinically acceptable range (± 0.5 °C),
• Especially among patients with fever (-1.44 °C to 1.46 °C for adults; -1.49 °C to 0.43 °C for children)
• For detection of fever, sensitivity was low 64% but specificity was high (96% [CI, 93% to 97%]; I2 = 96.3%; P < 0.001).

Limitations: High-quality data for some temperature measurement techniques are limited. Pooled data are associated with interstudy heterogeneity that is not fully explained by stratified and metaregression analyses. Their performance may be improved by taking repeated measurements over time, and they can be useful for measuring Temperature in children while they are sleeping.

Adults

We found a single study in 201 only adults in ICU that reported the compact digital axillar thermometer and the digital thermometer with probe obtained the highest overall valuation score.

Disclaimer:  the article has not been peer-reviewed; it should not replace individual clinical judgement and the sources cited should be checked. The views expressed in this commentary represent the views of the authors and not necessarily those of the host institution, the NHS, the NIHR, or the Department of Health and Social Care. The views are not a substitute for professional medical advice.