Original Investigation
September 5, 2023
Defining Usual Oral Temperature Ranges in Outpatients Using an Unsupervised Learning Algorithm
Catherine Ley, Frederik Heath, Trevor Hastie, et al
JAMA Intern Med. Published online September 5, 2023. doi:10.1001/jamainternmed.2023.4291
Question Can personalized temperature norms be defined to improve the clinical utility of oral temperature measurements?
Findings In this cross-sectional study, machine learning was applied to 618 306 adult outpatient encounters to define the usual or mean “normal” temperature as 36.64 °C. Using individual and temporal characteristics, the range of mean temperatures for the coolest to the warmest individuals was 36.24 °C to 36.89 °C.
Meaning These findings suggest that age, sex, height, weight, and time of day are factors that contribute to variations in individualized normal temperature ranges.
Abstract
Importance Although oral temperature is commonly assessed in medical examinations, the range of usual or “normal” temperature is poorly defined.
Objective To determine normal oral temperature ranges by age, sex, height, weight, and time of day.
Design, Setting, and Participants This cross-sectional study used clinical visit information from the divisions of Internal Medicine and Family Medicine in a single large medical care system. All adult outpatient encounters that included temperature measurements from April 28, 2008, through June 4, 2017, were eligible for inclusion. The LIMIT (Laboratory Information Mining for Individualized Thresholds) filtering algorithm was applied to iteratively remove encounters with primary diagnoses overrepresented in the tails of the temperature distribution, leaving only those diagnoses unrelated to temperature. Mixed-effects modeling was applied to the remaining temperature measurements to identify independent factors associated with normal oral temperature and to generate individualized normal temperature ranges. Data were analyzed from July 5, 2017, to June 23, 2023.
Exposures Primary diagnoses and medications, age, sex, height, weight, time of day, and month, abstracted from each outpatient encounter.
Main Outcomes and Measures Normal temperature ranges by age, sex, height, weight, and time of day.
Results Of 618 306 patient encounters, 35.92% were removed by LIMIT because they included diagnoses or medications that fell disproportionately in the tails of the temperature distribution. The encounters removed due to overrepresentation in the upper tail were primarily linked to infectious diseases (76.81% of all removed encounters); type 2 diabetes was the only diagnosis removed for overrepresentation in the lower tail (15.71% of all removed encounters). The 396 195 encounters included in the analysis set consisted of 126 705 patients (57.35% women; mean [SD] age, 52.7 [15.9] years). Prior to running LIMIT, the mean (SD) overall oral temperature was 36.71 °C (0.43 °C); following LIMIT, the mean (SD) temperature was 36.64 °C (0.35 °C). Using mixed-effects modeling, age, sex, height, weight, and time of day accounted for 6.86% (overall) and up to 25.52% (per patient) of the observed variability in temperature. Mean normal oral temperature did not reach 37 °C for any subgroup; the upper 99th percentile ranged from 36.81 °C (a tall man with underweight aged 80 years at 8:00 am) to 37.88 °C (a short woman with obesity aged 20 years at 2:00 pm).
Conclusions and Relevance The findings of this cross-sectional study suggest that normal oral temperature varies in an expected manner based on sex, age, height, weight, and time of day, allowing individualized normal temperature ranges to be established. The clinical significance of a value outside of the usual range is an area for future study.
