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Original articles
Accuracy of tympanic and infrared skin thermometers in children
  1. B F Paes1,
  2. K Vermeulen1,
  3. R M Brohet2,
  4. T van der Ploeg2,
  5. J P de Winter1
  1. 1Department of Pediatrics, Spaarne Hospital, Hoofddorp, The Netherlands
  2. 2Department of Research and Education, Linnaeus Institute, Spaarne Hospital, Hoofddorp, The Netherlands
  1. Correspondence to J P de Winter, Department of Pediatrics, Spaarne Hospital, Hoofddorp, The Netherlands; pdewinter{at}spaarneziekenhuis.nl

Abstract

Background Rectal measurement is considered a gold standard in many healthcare systems for body temperature measurement in children. Although this method has several disadvantages, an ideal alternative thermometer has not yet been introduced. However tympanic and infrared skin thermometers are potential alternatives.

Methods A prospective cohort study was performed including 100 children between 0 and 18 years of age admitted to the general paediatric ward of Spaarne Hospital in The Netherlands between January and March 2009. The objectives of this study are to evaluate the accuracy of tympanic and two types of infrared skin thermometers (Beurer and Thermofocus) compared to rectal measurement and furthermore to evaluate the influence of different variables on temperature measurements.

Results Compared to rectal measurement (37.56°C), the mean temperatures of the tympanic (37.29°C), Beurer (36.79°C) and Thermofocus (37.30°C) thermometers differed significantly (p<0.001). Mean and SD of differences between rectal temperature and temperature measured with these alternative devices varied significantly (p<0.001). Sensitivity, specificity, positive and negative predictive values for detecting rectal fever measured with the tympanic, Beurer and Thermofocus thermometers are unacceptable, especially for the Beurer thermometer. This difference in temperature between rectal and the alternative thermometers remained after stratification on gender, age, skin colour and otoscopic abnormalities.

Conclusions In this study the authors demonstrated that the tympanic, Beurer and Thermofocus thermometers cannot reliably predict rectal temperature. Therefore the authors do not advise replacement of rectal measurement as the gold standard for detecting fever in children by one of these devices. When rectal measurement is not used, the infrared skin thermometers appear to perform less well than tympanic measurements.

https://doi.org/10.1136/adc.2010.185801

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    Introduction

    The measurement of body temperature is essential to detect the presence of fever in children of all ages. Medical decisions concerning diagnosis, further investigation and treatment of children are partially based on body temperature. False negative measurement can lead to delayed detection of serious illness and false positive measurement can lead to an unnecessary diagnostic investigation. Since the introduction of body temperature measurements a variety of devices and methods have been introduced. Unfortunately, this has not yet led to the introduction of an ideal thermometer.

    What is already known on this topic

    • ▶ Body temperature measurement is important in decisions concerning diagnosis, further investigation and medical treatment of children.

    • ▶ Rectal measurement is still considered as the gold standard for body measurement despite several disadvantages.

    • ▶ Tympanic and infrared skin thermometers are potential alternatives for body temperature in children.

    • ▶ Infrared skin thermometers are relatively new alternatives for body temperature measurement.

    • ▶ Few studies have been performed on infrared skin thermometers. This is the first study performed in a general paediatric population.

    • ▶ Results of this study show that tympanic and infrared skin thermometers cannot replace rectal measurement as the gold standard for detecting fever in children.

    In general paediatric care the most commonly used method of measuring temperature in children is the measurement of rectal temperature. This method is considered as the gold standard in many healthcare systems around the world even though it has several disadvantages, including significant time consumption, discomfort, emotional distress and possibility of complications, such as perforation and transmission of micro-organisms.1,–,6 As a result of these disadvantages and the recommendations of the National Institute for Health and Clinical Excellence (NICE) clinical guideline7 some healthcare systems have abandoned rectal measurement in general paediatric care. In The Netherlands rectal measurement is still considered as the gold standard.

    Alternative methods are temperature measurements at the sublingual cavity and axillae. Studies performed on these measurement techniques show inconsistent results.8,–,18 Overall these methods are considered to be inaccurate and potentially hazardous in paediatric care.

    A relatively new and popular alternative for rectal measurement is the tympanic thermometer. This device measures the amount of infrared heat produced by the tympanic membrane by means of a sensor probe. The tympanic membrane shares its blood supply with the hypothalamus, the thermoregulatory centre of the human body. However, several comparison studies performed over recent years showed contradictory results.18,–,25

    The latest developed method of body temperature measurement is the infrared skin thermometer. With this method a sensor probe is used to measure the amount of infrared heat produced by the temporal arteries. Only a few studies have been performed on this topic, showing heterogeneous results as well.8 26,–,32

    The aim of the present study is to evaluate the accuracy and effectiveness of tympanic and infrared skin thermometers in paediatric care. Our objectives are (1) to evaluate the accuracy of tympanic and infrared skin thermometers, using rectal temperature as gold standard and (2) to evaluate the influences of the variables age, sex, skin colour and otoscopic abnormalities on temperature measurements.

    Materials and methods

    In this prospective study we included a sample of 100 children, admitted to the paediatric ward between January and March 2009, at Spaarne Hospital, Hoofddorp, The Netherlands. The study has been approved by means of written consent by the local research ethics committee (medical ethics committee Spaarne Hospital). Verbal informed consent for participation was obtained from all parents.

    During their clinical presentation the children were examined by two of our researchers (BP, KV). The following information about the children was collected: age, sex, skin colour and otoscopic abnormalities (otitis media or cerumen in the external auditory canal). During physical examination seven temperature measurements were performed, including two tympanic temperatures, two pairs of infrared skin temperatures and one rectal temperature. Rectal temperature was measured once owing to potential discomfort for the child. All temperatures were measured within 5 minutes. Rectal temperature was measured using the Terumo digital clinical thermometer (C402; Terumo Corporation, Tokyo, Japan). Tympanic temperature was measured using the FirstTemp Genius tympanic thermometer (3000A; Kendall Healthcare, Mansfield, Ohio, USA). The infrared skin temperatures were measured with the Beurer (FT40; Beurer, Ulm, Germany) and Thermofocus (700A2; Technimed, Varese, Italy) infrared skin thermometers. These infrared skin thermometers measure the amount of infrared heat produced by the temporal arteries. All thermometers were used as prescribed in the manuals of the devices.

    Statistical analysis

    SPSS 16.0 was used for statistical analyses. Tympanic and infrared skin temperatures were measured twice in each child. The mean value of these two measurements was used for comparison with rectal temperature. Data are expressed as mean values, SD and ranges. A p value ≤0.05 is considered statistically significant.

    The non-parametric Friedman analysis of variance test was used to compare mean temperature obtained by the four thermometers and mean differences between the rectal temperature and temperature measured by the other three devices. The correlation between rectal temperature and temperatures measured with tympanic and infrared skin thermometers were calculated using correlation coefficients and linear regression. Sensitivity, specificity, positive and negative predictive values were calculated for detecting rectal fever. For rectal temperature the generally used cut-off point for fever is 38.0°C. The influence of sex, age, skin colour and otoscopic abnormalities on temperature measurements were evaluated in a stratified analysis.

    Results

    Demographic and clinical data

    During the study period 100 children were included. They were presented with a variety of symptoms and diseases. The mean age of the children was 3.24 years, ranging from 2 weeks to 18 years of age. Fifty-eight children were younger than 2 years of age (58%). Fifty of the subjects were boys (50%). Nineteen children had skin colour showing a mixed origin (19%). The rest of the children had white skin (81%). No Asian or black children were included. Out of 200 tympanic measurements 60 were performed on ears showing otoscopic abnormalities (30%).

    Evaluation of tympanic and infrared skin thermometers

    Table 1 shows the means, SDs and ranges of temperature measured with rectal, tympanic, Beurer and Thermofocus thermometers. The highest mean temperature was measured with the rectal thermometer followed by the Thermofocus, tympanic and Beurer thermometers. With the Friedman test a significant difference (p<0.001) between mean temperatures measured with the four devices was found.

    View this table:
    Table 1

    Temperatures measured with rectal, tympanic, Beurer and Thermofocus thermometers

    Table 2 shows the mean values, SDs and ranges of difference between rectal temperature and temperature measured with the tympanic, Beurer and Thermofocus thermometers. These mean differences were, respectively, −0.271°C (SD 0.573°C), −0.767°C (SD 0.681°C) and −0.264°C (SD 0.595°C). These data showed that the Beurer infrared skin thermometer was the most inconsistent thermometer. Overall, the mean differences differed significantly (Friedman test p<0.001). The SDs of differences between rectal temperature and temperature measured with the other devices were large. This indicates that the alternative devices are not reliable in predicting rectal temperature.

    View this table:
    Table 2

    Difference between rectal temperature and temperature measured with tympanic, Beurer and Thermofocus thermometers

    Table 3 shows the correlation coefficients and linear regression between rectal temperature and temperature measured with the tympanic, Beurer and Thermofocus thermometers. The Pearson correlation coefficients (R) were respectively 0.827, 0.687 and 0.774. A correlation coefficient of 0.8 is generally considered as a strong and acceptable correlation. Therefore in our study we could only consider the correlation for rectal and tympanic temperature to be strong.

    View this table:
    Table 3

    Correlation and regression analyses between rectal temperature and temperature measured with tympanic, Beurer and Thermofocus thermometers

    Linear regression analysis was performed to investigate a linear relation between rectal measurement and measurement with the alternative thermometers. The corresponding scatter plots are given in figure 1. The regression coefficients were, respectively, 0.888, 0.426 and 0.661 for the tympanic, Beurer and Thermofocus thermometers. The residual unexplained percentages for the three thermometers were 4.0%, 20.8% and 12.5%. This indicated that the best goodness of fit can be found between rectal temperature and the tympanic thermometer. Furthermore, the Beurer infrared skin thermometer showed the lowest goodness of fit, confirming the poor correlation with the rectal thermometer.

    Figure 1
    Figure 1

    Scatter plots of rectal temperature versus temperature measured with tympanic (A), Beurer (B) and Thermofocus (C) thermometers. The solid line represents the reference line (R=1). The broken line represents the linear regression model.

    We calculated sensitivity, specificity, positive and negative predictive values for detecting rectal fever measured with the tympanic, Beurer and Thermofocus thermometers (table 4). For rectal temperature the generally used cut-off point for fever is 38.0°C. For the infrared skin thermometers, especially for the Beurer thermometer, these values are unacceptable.

    View this table:
    Table 4

    Sensitivity, specificity, positive and negative predictive values for detecting rectal fever (38.0°C) with the tympanic, Beurer and Thermofocus thermometers

    Evaluation of influence of variables on temperature measurement

    The second objective of our study was to evaluate the influence of the variables sex, age, skin colour and the presence of otoscopic abnormalities on temperature measurements. Using the aforementioned variables we split the population of 100 children four separate times into two groups: sex (male vs female), age (younger and equal to 2 years of age vs older than 2 years of age), skin colour (white vs mixed skin colour) and otoscopic abnormalities (presence vs absence). Table 1 shows the mean temperatures measured with the four thermometers for the complete group of 100 children. The mean temperatures differed significantly (Friedman test p<0.001). The mean temperatures measured with the four thermometers were also calculated for both groups of these variables. For both groups of all four variables we found the same significant differences (all p values <0.001) with the Friedman test as we did for the complete group of 100 children. This means that the significant difference between the four thermometers we found is not explained by the variables sex, age, skin colour and presence of otoscopic abnormalities.

    Discussion

    Body temperature is used in decisions concerning diagnosis, investigation and treatment of children. False measurements can have great consequences. An ideal thermometer should be accurate, safe, easy to use, comfortable and quick both for the child and the family. Throughout the years much research has been carried out in the field of thermometer design, but unfortunately this has not led to an ideal thermometer for physicians or patients.

    Rectal measurement is the most commonly used method, but has several disadvantages.1,–,6 The rather invasive procedure and cultural factors from parents and nurses make rectal temperature measurements difficult. Two alternative methods are the tympanic and infrared skin thermometers. Both methods are safe, easy to use, comfortable and quick. But the most important question that has to be answered positively to replace rectal measurement as the gold standard by a new method is the question ‘Is the method accurate?’ In our study we tried to find an answer to this question.

    Evaluation of tympanic and infrared skin thermometers

    The primary objective of our study was to evaluate the accuracy of the tympanic and infrared skin thermometers compared to rectal measurement of body temperature as gold standard. The first device we will discuss is the tympanic thermometer. This is a relatively new, but already generally used device in hospitals and at home. Our data suggest that the tympanic thermometer is more accurate than infrared skin thermometers in predicting rectal temperature. The SD of differences between rectal temperature and temperature measured with the alternative devices were large, including those for tympanic temperature. This indicates that the tympanic thermometer is not able to predict rectal temperature and therefore is not a good alternative for rectal measurement. These results are in agreement with several other studies.20 21 23 Craig et al20 reported in a systematic review that although mean differences between rectal and tympanic measurement were small, the wide limits of agreement they found indicated that tympanic measurement was inaccurate and could not replace rectal measurement. Other studies reported the tympanic thermometer as accurate and recommended its use in paediatric care.18 19

    Infrared skin thermometers are the latest developed devices that measure the amount of infrared heat produced by the temporal arteries. The Beurer infrared skin thermometer is the second device we will evaluate. In our study this thermometer is the most inconsistent device. In general this thermometer measured too low a body temperature. This discrepancy increased with increasing body temperature.

    The third thermometer in our study is the Thermofocus infrared skin thermometer. This type of infrared skin thermometer was more accurate than the Beurer infrared skin thermometer, but less accurate than the tympanic thermometer. Both infrared skin thermometers had a large SD of differences between skin and rectal temperature. This can lead to false measurements with serious consequences.

    Only a few studies examined the accuracy of infrared skin thermometers. Our data support the majority of these studies performed in children.8 28,–,30 32 These studies, mostly performed in children younger than 2 years of age, demonstrated data that suggested that infrared skin thermometers were unreliable in predicting rectal fever. These studies also found unacceptable differences and the authors concluded that rectal measurement cannot be replaced by infrared skin measurement as gold standard. Only De Curtis et al26 considered infrared skin measurement as a comfortable and reliable way of body temperature measurement in newborns.

    In general, tympanic and infrared skin thermometers use a correction factor to calculate the rectal temperature. New cut-off points could possibly improve the measurements of the thermometers, but the variance will remain large. Therefore these thermometers are still not able to predict rectal temperature accurately.

    Thermometers have to be used specifically according to instructions to obtain correct measurements. To measure tympanic temperature the sensor probe needs to measure the tympanic membrane directly by lifting up the ear. To measure infrared skin temperature the Beurer infrared skin thermometer needs to be slid along the forehead and the Thermofocus infrared skin thermometer needs to be used at an exact distance from the forehead. The children were examined by two of our researchers who were experienced in operating these devices. When these devices are used by inexperienced people (such as parents), more unreliable measurements may be obtained; but when also used by professionals unreliable measurements can be obtained, frequently caused by children's lack of cooperation.

    Evaluation of influence of variables on temperature measurement

    The second objective of our study was to evaluate the influence of sex, age, skin colour and otoscopic abnormalities on temperature measurements. In our study the differences between rectal measurement and measurement with tympanic or infrared skin thermometers were significant, regardless of the influences of sex, age, skin colour and otoscopic abnormalities. There were only two other studies that examined the influences of sex, age and race on infrared skin measurements.28,30 These variables had an insignificant effect on the inaccuracy of infrared skin thermometers in these studies. There is a paucity of studies that have examined the influence of otoscopic abnormalties. The presence of these abnormalities did not alter the accuracy of tympanic measurement.33,–,36 These results were confirmed in our study.

    There are a few limitations to our study. We did not used a measurement of true body temperature as gold standard. In our study tympanic and infrared skin thermometers were compared to rectal measurement. Some studies presented data that rectal measurement is not the most reliable method for measuring the core temperature of the human body.36,–,40 These studies considered measurement of the pulmonary artery, bladder or oesophagus as more reliable alternatives and as the gold standard. In our study we tried to find an alternative method that can be used in the general paediatric care. These alternative techniques are only used on intensive paediatric or neonatal care units. These techniques are invasive and can lead to severe complications and discomfort. Therefore we did not consider them as an alternative for rectal measurement in our study. Some healthcare systems around the world abandoned rectal measurement from general paediatrics care according to the recommendations of the NICE clinical guideline.7

    During physical examination seven temperature measurements were performed. We measured rectal temperature only once owing to potential discomfort for the child. Tympanic and infrared skin thermometers are relatively easy and comfortable to use and therefore we measured these temperature twice in each child. The single measurement of rectal temperature could be a limitation of our study. Rectal measurement is an easy method and relatively stable temperature in time and therefore we found a single rectal measurement acceptable.

    We used a general paediatric population with a large range of age. Therefore the results of this study can be translated to general paediatric populations in other hospitals. Most other studies on infrared skin measurement in children were performed in newborns or toddlers.8 26 28 29 32 Their results cannot be translated to other age groups.

    Conclusions

    In this study we demonstrated that the tympanic, Beurer and Thermofocus thermometers cannot reliably predict rectal temperature. The Beurer infrared skin thermometer is the most inconsistent thermometer. Therefore we do not advise replacing rectal measurement as the gold standard for detecting fever in children by one of these devices. However, when rectal measurement is not used, the infrared skin thermometers appear to perform less well than tympanic measurements.

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    View Abstract

    Footnotes

    • Ethics approval This study was conducted with the approval of the ethics committee of Spaarne Hospital, Hoofddorp.

    • Provenance and peer review Not commissioned; externally peer reviewed.