A Normal Temperature May Not Be What We Were Taught

Abstract & Commentary

By Mary Elina Ferris, MD, Clinical Associate Professor, University of Southern California. Dr. Ferris reports no financial relationship to this field of study.

This article originally appeared in the March 2006 issue of Internal Medicine Alert. It was reviewed by the physician editor, Stephen Brunton, MD, and peer reviewed by Gerald Roberts, MD.

Synopsis: Mean oral temperatures decline with age, ranging from 97.3°F at 6 am to 97.8°F at 10 pm in persons older than 65 years. The majority of both nursing home and community elderly have normal mean temperatures below 98.6°F.

Source: Gomolin IH, et al. Older is Colder: Temperature Range and Variation in Older People. J Am Geriatr Soc. 2005;53:2170-2172.

Oral temperatures for 100 nursing home residents were measured on 3 consecutive days using a single digital electronic thermometer, and once during mid-day office visits for 50 community dwellers. Nursing home residents all had their measurements on the same days at 3 times: 6 am, 4 pm, and 10 pm, and had not taken antipyretics, nor taken anything by mouth for 30 minutes before the reading. Average age was 80.7 years (range, 65-98 years old); 111 were women and 39 men. No statistical differences were present between the two measurement sites or genders. Although the individual range of measurements was 94.0°F to 99.6°F, the variability of the mean for each time period was less than 0.82°F. Mean oral temperatures declined with age, from 98.2°F for age 65-74 years old to 97.4°F for age 85 years and older.

Commentary

This simple yet important study confirms that the majority of healthy elderly persons have normal oral temperatures lower than the usually accepted 98.6°F, ranging from 98.2°F down to 97.4°F. Geriatric specialists have suggested that recognition of fevers in this group should start at 99-100°F, and should especially be compared to the baseline established for that particular patient, since we know the normal reading can decline with advancing age.1 The maxim that older patients have "atypical presentations of disease" may actually represent our ignorance of their normal baseline measurements.

In fact, the accepted normal temperature of 98.6°F may not be accurate for younger persons either. Previous studies have shown that 98.2°F is a more accurate mean oral temperature in healthy adults aged 40 years or younger, with a variability of 0.9°F.2 There are also clear diurnal variations of temperature, with lowest temperatures at 6 am and highest at 4-6 pm. As we accumulate more specific data to adjust our expectations of normal values, we should be able to assess developing diseases more accurately in the future.

References

1. Castle SC, et al. Fever Response in Elderly Nursing Home Residents: Are the Older Truly Colder? J Am Geriatr Soc. 1991;39:853-857.

2. Mackowiak PA, et al. A Critical Appraisal of 98.6 Degrees F, the Upper Limit of the Normal Body Temperature, and Other Legacies of Carl Reinhold August Wunderlich. JAMA. 1992;268:1578-1580.