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. 2018 Feb 23;8(1):3526.
doi: 10.1038/s41598-018-22020-6.

Body temperature measurement in mice during acute illness: implantable temperature transponder versus surface infrared thermometry

Jie Mei  1 , Nico Riedel  2 , Ulrike Grittner  3   4 , Matthias Endres  1   3   5   6 , Stefanie Banneke  7 , Julius Valentin Emmrich  8
Affiliations

Body temperature measurement in mice during acute illness: implantable temperature transponder versus surface infrared thermometry

Jie Mei et al. Sci Rep. .

Abstract

Body temperature is a valuable parameter in determining the wellbeing of laboratory animals. However, using body temperature to refine humane endpoints during acute illness generally lacks comprehensiveness and exposes to inter-observer bias. Here we compared two methods to assess body temperature in mice, namely implanted radio frequency identification (RFID) temperature transponders (method 1) to non-contact infrared thermometry (method 2) in 435 mice for up to 7 days during normothermia and lipopolysaccharide (LPS) endotoxin-induced hypothermia. There was excellent agreement between core and surface temperature as determined by method 1 and 2, respectively, whereas the intra- and inter-subject variation was higher for method 2. Nevertheless, using machine learning algorithms to determine temperature-based endpoints both methods had excellent accuracy in predicting death as an outcome event. Therefore, less expensive and cumbersome non-contact infrared thermometry can serve as a reliable alternative for implantable transponder-based systems for hypothermic responses, although requiring standardization between experimenters.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Line graphs showing body core and surface temperature across lipopolysaccharide (LPS)- and saline-treated groups for up to 7 days post-treatment. (a) Temperature profile obtained by implantable radio frequency identification (RFID) transponders and infrared thermometer 2 (n = 380; LPS-treated, 251; saline-treated, 129). (b) Temperature profile obtained by implantable RFID transponders and infrared thermometer 1 (n = 55; LPS-treated, 33; saline-treated, 22.). Blue, saline-treated control animals; red, LPS-treated animals; solid line, core temperature; dotted line, surface temperature; grey arrow, time of LPS/saline injections. Data shown are means ± 95% CI.
Figure 2
Figure 2
Kaplan-Meier curve showing cumulative survival across lipopolysaccharide (LPS)- and saline-treated animals for up to 7 days post-injection. Blue, saline-treated control mice (n = 151, n(dead) = 0); red, LPS-treated mice (n = 284, n(dead) = 30).
Figure 3
Figure 3
Prediction of core temperature from surface temperature using a mixed effects model. (a) Surface temperature measured by thermometer 2, plotted against the corresponding core temperature (n = 124, ICC = 0.80 (95%CI: 0.79–0.81)) and (b) surface temperature measured by thermometer model 1, plotted against the corresponding core temperature (n = 53, ICC = 0.89 (95%CI: 0.88–0.90)) show a positive non-linear correlation. A fitted mixed effects model was used to predict the corresponding core temperature from surface temperature. Marginal R2 (R2m): 0.65, conditional R2 (R2c): 0.81; Black solid line, fit line of the mixed effects model showing the core temperature predicted from surface temperatur.        Fitlinein(a),y=−0.12×(x−30)2+0.92×(x−30)+35.48        fitlinein(b),y=−0.12×(x−30)2+0.8×(x−30)+36.36
Figure 4
Figure 4
Predicting death using threshold models trained with core or surface temperature. (a) Core temperature (n = 160, number of dead animals = 13) or (b) surface temperature (n = 372, number of dead animals = 28) at 36 hours after the first injection was plotted against baseline temperature values. Blue and red dots represent measurements of survived and dead animals, which were used in the training, testing and validation of the prediction model, with one dot indicating measurements of one animal. Black solid lines indicate the decision boundaries determined by the prediction model trained with core or surface temperatures. If an animal’s body temperature falls into the area below the decision boundary (i.e., core temperature <28.1 °C or surface temperature <24.3 °C), the animal is predicted to die at a later time point. Applying a combination of the two thresholds would have allowed for early termination of experiments before animals experienced further distress for 13 out of 19 animals, which died at later time points during the study. Applying thresholds individually would have resulted in early termination of experiments for 4 out of 7 transponder-implanted animals or 12 out of 19 animals with surface temperature recordings, respectively.
Figure 5
Figure 5
Illustration of the measurement modalities used to obtain core and surface temperature data. (a) Size comparison of a temperature transponder to a 20-cent coin. (b) Mouse with the ano-genital area exposed. Red circle depicts perianal region used as the site for surface temperature acquisition.
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