Normal mean oral temperature in Indians: 98.0°F

Aim: To find out the normal mean oral temperature in the Indian population as per a longitudinal study. Background: 98.6°F is generally accepted as normal body temperature as defined by Wunderlich (1868) and later challenged by Mackowiak (1992) and Protsiv (2020) who concluded it as 98.2°F based on cross-sectional studies. Hence, the normal body temperature at present needs quantification as per a longitudinal study in Indians. Patients and Methods: A longitudinal study on the healthy population of Northern India was followed-up over 1 year. Participants were advised for self-monitoring of oral temperature with a standard digital thermometer in either left or right sublingual pocket and record it in the thermometry diary. The study was considered complete if the participant had all three phases of the study (i.e., non-febrile, febrile and post-febrile phases) or completed the duration of the study. Results: The mean oral temperature of the participants (n = 144) during the non-febrile and post-febrile phases (temperature readings = 6543) were 98.0°F (standard deviation [SD], 0.61) and 98.01°F (SD, 0.60), respectively (P < 0.001). With the diurnal variability, the morning (am), noon (an) and afternoon (pm) mean temperatures were 97.91°F, 98.08°F and 98.27°F (P < 0.001), respectively, during the non-febrile phase. Similar trends were observed in variability among men and women, seasons and across post-febrile phase. Conclusions: The mean oral temperature was 98.0°F (SD, 0.61). The temperature was as low as 96.9°F and as high as 99.1°F. The temperature during the post-febrile phase was found to be higher than the non-febrile phase temperature such as pm over an and am, women over men, summer over other seasons in the non-febrile phase and spring over others in the post-febrile phase.