Two readers question the usual definition of fever:
Is there any validity to statements by patients that their basal temperature is always low and they never run a fever?
—Stuart O. Miller, MD, Charlotte, N.C.

Many patients claim to be ill even though their temperature is normal, saying “My normal body temperature is 97.5°F, so I consider anything above that to be a fever for me.” I realize that there is a range of normal in medicine, but I certainly would not consider a temperature of 98.6°F to be a fever in any patient.
—Joseph E. Badolato, DO, Ridgefield, Wash.

The 98.6°F temperature benchmark was determined in 1861 by Dr. Carl Wunderlich, a German physician, who after measuring a million temperatures in healthy adults found the average to be 37°C (98.6°F). A 1992 study of adults under 40 found the actual mean oral temperature to be 98.2°F (JAMA. 1992;268:1578-1580). More recent data have further challenged what is normal, particularly among the elderly. In a comparison of oral temperatures in young subjects vs. elderly nursing-home residents, Gomolin et al found that older people have lower afternoon temperatures (97.4°F +/- 0.93° for the elderly vs. 97.8°F +/- 0.92° in the young) and less diurnal variation than young subjects (J Am Med Dir Assoc. 2007;5:335-337). Few subjects (young or old) even reached the 98.6°F benchmark during any of the measurements. This evidence and other studies suggest that at least in the elderly, the threshold for recognizing fever may need to be lowered (say to 99°F or 100°F) or be based on a significant increase in each patient’s established basal temperature.
—Susan Kashaf, MD, MPH (124-8)