Human body temperature to give the most accurate assessment of core body temperature, particularly in hypothermia. In the early 2000s, ingestible thermistors in capsule form were produced, allowing the temperature inside the digestive tract to be transmitted to an external receiver; one study found that these were comparable in accuracy to rectal temperature measurement. In the 19th century, most books quoted "blood heat" as 98 °F, until a study published the mean (but not the variance) of a large sample as . Subsequently that mean was widely quoted as "37 °C or 98.4 °F" until editors realised 37 °C is closer to 98.6
Human body temperature raised, the result is a fever. Most fevers are caused by infectious disease and can be lowered, if desired, with antipyretic medications. An early morning temperature higher than or a late afternoon temperature higher than is normally considered a fever, assuming that the temperature is elevated due to a change in the hypothalamus's setpoint. Lower thresholds are sometimes appropriate for elderly people. The normal daily temperature variation is typically , but can be greater among people recovering from a fever. An organism at optimum temperature is considered "afebrile" or "apyrexic", meaning "without fever". If temperature is raised, but the setpoint