A critical appraisal of 98.6 degrees F, the upper limit of the normal body temperature, and other legacies of Carl Reinhold August Wunderlich.

OBJECTIVE To evaluate critically Carl Wunderlich's axioms on clinical thermometry. DESIGN Descriptive analysis of baseline oral temperature data from volunteers participating in Shigella vaccine trials conducted at the University of Maryland Center for Vaccine Development, Baltimore. SETTING Inpatient clinical research unit. PARTICIPANTS One hundred forty-eight healthy men and women aged 18 through 40 years. MAIN MEASUREMENTS Oral temperatures were measured one to four times daily for 3 consecutive days using an electronic digital thermometer. RESULTS Our findings conflicted with Wunderlich's in that 36.8 degrees C (98.2 degrees F) rather than 37.0 degrees C (98.6 degrees F) was the mean oral temperature of our subjects; 37.7 degrees C (99.9 degrees F) rather than 38.0 degrees C (100.4 degrees F) was the upper limit of the normal temperature range; maximum temperatures, like mean temperatures, varied with time of day; and men and women exhibited comparable thermal variability. Our data corroborated Wunderlich's in that mean temperature varied diurnally, with a 6 AM nadir, a 4 to 6 PM zenith, and a mean amplitude of variability of 0.5 degrees C (0.9 degrees F); women had slightly higher normal temperatures than men; and there was a trend toward higher temperatures among black than among white subjects. CONCLUSIONS Thirty-seven degrees centigrade (98.6 degrees F) should be abandoned as a concept relevant to clinical thermometry; 37.2 degrees C (98.9 degrees F) in the early morning and 37.7 degrees C (99.9 degrees F) overall should be regarded as the upper limit of the normal oral temperature range in healthy adults aged 40 years or younger, and several of Wunderlich's other cherished dictums should be revised.