What is the most reliable method for measuring core body temperature?

Measuring core body temperature accurately is crucial in clinical settings for understanding a patient's health status. The rectal temperature measurement is considered the most reliable method for assessing core body temperature. This is because the rectum is anatomically closer to the body's core, thus providing a measurement that closely reflects the internal body temperature. It is less influenced by external factors, such as ambient temperature or recent oral intake, which can affect other methods.

In contrast, oral temperature measurement can be affected by recent food or fluid intake, breathing patterns, or even the presence of oral pathology. Armpit (axillary) temperature measurement tends to be less accurate since it can fluctuate based on external factors, such as the temperature of the surrounding environment and individual conditions, making it a less reliable indicator of core temperature. The temporal artery measurement, while increasingly used for its convenience and speed, is also susceptible to external influences and does not always provide a true reflection of core body temperature compared to rectal measurements.

Therefore, rectal temperature measurement is typically the preferred method, especially in situations requiring precise temperature readings, such as in infants, during surgical procedures, or for critically ill patients.