Agreement of telemetric temperature capsules ingested 48 hours apart

Telemetric temperature capsules are frequently utilized to measure deep body temperature. Whereas most methods to measure temperature are conducted at a single site (e.g., rectal temperature), the location of ingested telemetry capsules varies. If distinct regions of the gastrointestinal tract have different temperatures, the measurements obtained using telemetry capsules will vary accordingly. This study examined the agreement of two telemetric temperature capsules in fifty-seven Army Ranger School students ingested 64 and 16 h before a cool weather waterborne movement. Twenty-one subjects (37%) (age: 25 ± 4, weight: 81±7 kg) retained both capsules. Subjects completed activities that could increase (e.g. exercise) and decrease (e.g. cold water immersion) body temperature. Agreement between the two capsules was assessed through concordance and Bland Altman analysis using a linear mixed model. Bias between the two capsules was low (0.01 °C, SE = 0.03, before a neck-deep immersion river crossing and -0.09 °C, SE = 0.08, after the river crossing), but there were large differences in the variance components (0.044 vs 0.155 total variance for the pre-crossing vs the post-crossing data). The 95% Limits of Agreement indicate that discordance between the two capsules was lower before the river crossing (-0.40 to +0.42 °C) than after (-0.86 to +0.68 °C). In summary, this study examined telemetry capsule agreement with more time between capsule ingestion (48 h) in a larger sample size than most previous studies on the topic, and found notable (95% LoA>0.4 °C) variability between the two capsules which was exacerbated after crossing a cold river. Differences in gastrointestinal location of telemetry capsules can introduce variability into the measurement of deep body temperature due to regional temperature differences. This variability may be acceptable for some study designs, but unacceptable when small changes in temperature are important to detect. If the convenience of telemetric temperature capsules is desired, an alternative is to use the capsule as a rectal suppository.