Selecting thermometer accuracy in estimating the postmortem interval using body temperature-based methods: A technical report

BACKGROUND: Establishing the postmortem interval of a deceased individual with the highest possible accuracy is critical for the objective investigation of criminal homicide. It is well known that instrumental error in measuring a parameter used in calculations is one of the primary sources of error in any computational method. However, in body temperature-based methods for estimating postmortem interval, the accuracy of temperature measurement adequate for forensic medicine has not been established.

AIM: The work aimed to develop practical recommendations for selecting a measuring instrument for postmortem examination based on the impact of body temperature measurement accuracy and environmental factors on the error in calculated postmortem interval.

METHODS: Using the phenomenological mathematical model by Henssge et al., changes in postmortem body temperature were predicted in various diagnostic zones (brain, liver, rectum) at ambient temperatures of 0 °C and 20 °C. The method’s instrumental error was calculated for these conditions using thermometers with accuracies of 1 °C, 0.1 °C, and 0.01 °C. The results were expressed as both absolute and relative errors (%), which were calculated as the ratio of error to the postmortem interval at which it was obtained.

RESULTS: The highest relative errors were reported during the early phase of postmortem cooling and during the stage of temperature equalization between the body and the environment. In all cases, using thermometers with an accuracy of 1 °C resulted in a relative error of more than 15% of the postmortem interval value. Moreover, the use of thermometers with an accuracy of 0.1 °C or 0.01 °C ensured a relative instrumental error of no more than 5% throughout the modeling period (2–24 hours).

CONCLUSION: According to biomedical research guidelines, satisfactory results can only be achieved when body and ambient temperatures are measured with an accuracy of 0.1 °C or 0.01 °C. For practical convenience, we implemented the algorithm for calculating the instrumental error in postmortem interval estimation in the form of a Microsoft Excel spreadsheet.