Evaluation of core body temperature is an essential component of the feline physical examination and is considered one of the key vital signs. Traditionally, the normal feline core body temperature range as measured with a rectal thermometer has been considered to be 100.0-102.5⁰F (37.7-39.2⁰C), but there is little evidence to support this reference interval, and the conditions under which this range was established are unknown.

In this study of 200 healthy adult indoor cats whose rectal temperatures were measured in animal shelters (n = 179), veterinary clinics (n = 3), and private homes (n = 18), the animals ranged in age from 1-16 years, with a median age of 3 years. At least 6 hours were allowed to elapse between the time the animal entered the facility and the time the rectal temperature was measured to permit acclimation. The ambient temperature in the facilities ranged from 68.5-87.5⁰F (20.3-30.8⁰C), and the rectal temperatures obtained did not correlate significantly with the ambient temperature. All cats’ rectal temperatures were obtained using the same brand of digital rectal thermometer, and all environmental temperatures were measured with the same brand of ambient scanning thermometer.

These researchers found that the normal range of rectal temperature in the study population of healthy indoor adult cats was 98.1-102.1⁰F (36.7-38.9⁰C), which is lower and wider than the reference intervals listed in a number of veterinary textbooks and in published articles. The mean + standard deviation of feline rectal temperature found in this study was 100.1 + 1.01⁰F (37.8+0.6⁰C). Healthy juvenile and geriatric cats, and cats that live outdoors or under stressful conditions such as confinement with unaffiliated dogs, could have different reference ranges for core body temperature, so additional studies are needed in these groups. In this study, no significant difference was found between rectal temperatures obtained from cats in shelters and those measured in cats in private homes or veterinary clinics.

As both hypothermia and pyrexia are associated with significant disease states, morbidity, and even mortality in feline patients, this new reference interval established for adult cats confined indoors changes the criteria for diagnosis of these conditions. A cat whose core body temperature as measured with a rectal thermometer is at the lower end of the new reference range would be considered hypothermic based on previously published reference ranges, and one whose core body temperature falls at the higher end of the new reference range would not be considered pyrexic with respect to most of the older reference intervals. Regardless of the reference interval used, the core body temperature must be interpreted in light of the patient’s history and other clinical signs. The new reference interval also has important implications for monitoring of anesthetized cats, as maintaining core body temperature as close to normal as possible for the patient is an important goal in the support of anesthetized individuals, and both hypo- and hyperthermic states are possible in anesthetized cats.  [PJS]