Should 37°C be Considered the Benchmark for ‘Normal’ Oral Temperature?
BACKGROUND AND PURPOSE:
- The “normal” oral temperature of 37°C was established in 1851 based on a population mean
- Ley et al. (JAMA Internal Medicine, 2023) determined normal oral temperature ranges by age, sex, height, weight, and time of day
METHODS:
- Cross-sectional study
- Temperature values from all adult outpatient encounters at Stanford Health Care
- Application of LIMIT (Laboratory Information Mining for Individualized Thresholds), a machine learning algorithm that filters data sets to generate a ‘normal’ distribution
- Population
- All adult outpatient encounters that included temperature measurements in a large medical care system
- Exposures
- Primary diagnoses | Medications | Age | Sex | Height | Weight | Time of day | Month
- Study design
- LIMIT removed overrepresented primary diagnoses in the temperature distribution tails leaving diagnoses unrelated to temperature
- Mixed-effects model used to
- Identify independent factors associated with normal oral temperature
- Generate normal temperature ranges
- Primary outcome
- Normal temperature ranges by exposure
RESULTS:
- 618,306 patient encounters with temperature data
- Removed by LIMIT: 35.9%
- Encounters removed were primarily linked to infectious diseases and type 2 diabetes
- 396,195 included patient encounters | 126,705 patients
- Mean age: 52.7 (SD, 15.9) years | Women: 57.35%
- After running LIMIT, the mean temperature was 36.64°C (SD, 0.35°C)
- Central 95% of these temperatures were between 35.95°C and 37.33°C
- Age, sex, height, weight, and time of day accounted for variability in temperature
- Overall: 6.86%
- Per patient: 25.52%
- Mean normal oral temperature did not reach 37°C for any subgroup
- The upper 99th percentile ranged from
- 36.81ºC (a tall man with underweight aged 80 years at 8:00 am)
- 37.88ºC (a short woman with obesity aged 20 years at 2:00 pm)
CONCLUSION:
- The mean usual or “normal” oral temperature is 36.64°C
- Body temperature varies as expected by age, weight, sex, and time of day
- The authors state
Given that body temperature is a rough marker of metabolic rate, it is reasonable to conclude that metabolic rate has decreased over time
Reasons for such a decrease in metabolic rate remain speculative but likely include a reduction in inflammation, due in part to reduced chronic infections, improved dental care, and access to anti-inflammatory medications such as statins and nonsteroidal anti-inflammatory drugs
Learn More – Primary Sources:
Defining Usual Oral Temperature Ranges in Outpatients Using an Unsupervised Learning Algorithm
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