Measuring body temperature is one of the oldest methods to discern a problem in both medical and nonmedical fields;1 in fact, proper functioning of the body is dependent upon keeping the body temperature within the normal range (37.2°C–37.8°C), because an increase (>41.5°C) or decrease (>30°C) in body temperature can lead to death.2,3 Accurate determination of body temperature in critically ill patients is a fundamental requirement for initiating the proper process of diagnosis, and also therapeutic actions. For this purpose, measuring temperature with mercury, tape, digital, and tympanic thermometers are currently the commonly used methods.4 Each method has many advantages and some disadvantages, so selecting the proper thermometer and a more rigorous method is crucial.1 

For measuring body temperature, eight locations have been considered, which include the nasopharynx, esophagus, pulmonary artery, rectum, axillae, tympanic membranes, legs, and bladder. Ideally, it is better, if possible, that measurement of temperature be done by a thermometer that is noninvasive, hygienic, convenient, and affordable, and also the measured temperature value would be close to the core body temperature eventually. In fact, the gold standard method for measuring the core body temperature is by way of the pulmonary artery approach,5but this method has some restrictions such as being invasive and applicable only under special circumstances, in critical care wards and for unconscious patients.1,6 Another accurate method, which is accepted as the standard approach, is the nasopharyngeal method, which is noninvasive and in which the temperature is measured by inserting a sensitive probe into the external opening of the nose and directing it to the pharynx, between the nose and ears.5,7–9

Nowadays, the most common sites for measuring body temperature by local sensors include: oral cavity, tympanic membranes, pulmonary artery, axillae, rectum, esophagus, and gastrointestinal tract. Mouth, forehead, ears, and axillae are the most accessible parts of the body that have mostly been used by specialists in internal medicine to measure temperature; these sites show body temperature faster and easier, and in a noninvasive way, but the most appropriate method of measurement is still controversial.4,10

Several studies have been conducted for determining the most correct and accurate ways of measuring body temperature. In this regard, some authors have recommended the use of tympanic thermometers while others have not.1 Dzarr et al indicated that tympanic temperature is equal to core body temperature.11However, Rubia-Rubia et al introduced axillary temperature measurement method as the best method and rejected the forehead approach.1 In this respect, Edelu et al recommended not using the axillary method.12The results of Mazerolle et al’s study showed that the oral method could not reflect the core temperature of the body correctly,10 while Chue et al and Barnett et al announced that temperature measurement by tympanic and oral methods can correctly show the core body temperature.13,14

source:  Accuracy and precision of four common peripheral temperature measurement methods in intensive care patients. Simin Asadian,1 Alireza Khatony,1 Gholamreza Moradi,2 Alireza Abdi,1 and  Mansour Rezaei3. Published online 2016 Sep 1. doi: 10.2147/MDER.S109904. PMCID: PMC5012839. PMID: 27621673