Diagnostic Accuracy of Non-Contact Infrared Thermometer in Comparison with Mercury Thermometer and Digital Thermometers
Authors: Bright Binu , PS Anu , Kumar KP Gireesh 
Published: March 2023

BACKGROUND: Body temperature is a vital parameter in patient assessment. Fever is a common presentation in patients arriving at all health care setups. [1] It is a transient pathological state characterised by a disturbance in the hypothalamus thermoregulation system and, as a result, an increase in the body's temperature above the normal range. Normal body temperature values range from 36.5 to 37.4 °C depending on physiological variations, patient characteristics, and measurement sites. [2] Fever is a sign of underlying pathology – infection, infestation, inflammation, autoimmune diseases, malignancy, medication adverse reaction, intracranial haemorrhage or pulmonary embolism. Fever is also an important symptom in COVID-19 patients, typically appearing 12–14 days after exposure. And that made screening patients for elevated body temperature an essential initial triaging tool during the pandemic. [3] [4] A clinical thermometer is the equipment used for measuring body temperature. Several thermometers are available, each with its advantages, disadvantages, applicability, reliability and sensitivity. [5] Mercury-in-glass thermometers were the standard way to measure temperature for many years. They were taken off the market in the late 2000s because mercury is toxic to the environment. After that, many thermometers came into use, including digital, tympanic or axillary thermometers and non-contact infrared thermometers. Presently digital thermometers occupy the bedside at both homes and hospitals, including clinics. [6] [7] [8] The COVID-19 pandemic brought in, at large scales, the use of a non-contact infrared thermometer as a screening tool to measure body temperature. [9] [10] Our knowledge of the relative performance of different types of thermometers, including differences in temperature measured, is limited despite the essential role they play in clinical practice. So, it's essential to understand how different thermometers work and how accurate they are at making diagnoses. [11] [12] This is especially crucial considering the triage significance of fever measurement in clinical settings, especially emergency care, to refer patients to appropriate care pathways.
OBJECTIVES: To evaluate the diagnostic accuracy of non-contactable infrared thermometers in comparison with mercury and digital thermometers.
METHODOLOGY: The prospective observational study was conducted on 210 patients of both genders, of all age groups, presenting with or without fever to the ED of AIMS, Kochi, and a quaternary during the period from January to June 2022. The data we collected and statistically analysed from the study population are age, sex, presenting complaints, co-morbidities, heart rate, blood pressure, respiratory rate, SpO2, and body temperature being simultaneously measured with mercury, digital and non-contact infrared thermometers. The temperature of all patients was recorded using mercury, a digital thermometer placed in each axilla simultaneously, and a non-contactable infrared thermometer on the forehead. Mercury in glass thermometer was placed in axilla with the bulb of the thermometer in the tip of the axilla for 2 minutes. The digital thermometer was placed in a similar fashion in the other axilla and removed from the axilla after the beep was heard and temperature displayed was noted. The infrared thermometer is placed near the forehead or wrist, with a 5cm gap between the two. The trigger button is gently pressed, and the temperature shown on the LCD screen is recorded.
RESULT: The study group included 53% males and 47% females. 58% belonged to the age group between 46 and 75 years, 30% between 16 and 45 years of age, 11% between 76 and 99 years and 1% below 15 years of age. Fever was present in 20.5% of the patients and the rest had other symptoms like vomiting, diarrhoea, cough, dyspnoea, fatigue, weakness, body pain and pedal oedema. 57% had two comorbidities, 29% were with more than 2 comorbidities while 14% had no known comorbidities. The body temperatures measured by mercury and digital thermometers were almost identical – Normal in 85.5%, above normal in 14% and below normal in 0.5%; but with a non-contact infrared thermometer, the same were 97.5%, 2.5% and 0% respectively.
DISCUSSION: This study is highly relevant in the current scenario where the pandemic situation is almost over and a lot of institutions who invested in NCIT have started considering them for use as alternative devices for recording temperature. In our study, non-contact infrared thermometer failed in detecting fever in several affected patients, or misread normal temperature as elevated and was not capable of detecting hypothermia. Additional research is required to compare its accuracy and precision to other invasive and non-invasive core body temperature testing methods. The study finding of a rise in heart and respiratory rates in fever patients, though non-specific, concur with inferences from other similar studies.
CONCLUSION: Our study concluded that the accuracy of non-contactable infrared thermometers is less reliable than mercury and digital thermometers for routine clinical practice. Though, the non-contact infrared thermometer was widely being used during the pandemic scenario, our study results do not favour its use other situations like the clinics, intensive care units or emergency departments.

Key words: [Mercury, Digital, Infrared, Thermometer, COVID, Healthcare technology]