Are We Wrong About Fevers?

Stephanie K. Nguyen


October 19, 2018

What temperature is considered a fever?

A resident asked me that question last week. I responded with "100.4° F (38° C) and higher." I never asked about the evidence that was used to determine that benchmark.

I was directed to read about a study conducted by Dr Carl Wunderlich from the late 1800s. The study recorded the axillary temperatures of over 25,000 patients at the University of Leipzig over 16 years. He published his results in 1868 and reported that 98.6° F (37° C) was a normal body temperature, with fever starting at 100.4° F (38° C). Wunderlich also showed that temperature tended to be lowest in the morning and peaked in the evening.

In 1992 Mackowiak and colleagues analyzed the temperatures of 148 healthy volunteers and found the average temperature to be 98.2° F (36.8° C). This study also supported Wunderlich's statement that body temperature varies diurnally, with a 6 AM nadir and 4-6 PM peak.

More recently, a crowdsourced study published in the Journal of General Internal Medicine reported that the mean temperature for males was 97.7° F (36.5° C), and the mean female temperature was 97.88° F (36.6° C). They defined fever as the 99th percentile of normal temperatures, which they reported to be 99.86° F (37.7° C).

Seeing that several studies now refute Wunderlich's benchmark of normal temperature being 98.6° F (37° C) makes me interested to see what other "accepted facts" we are being taught in medicine. It's rather concerning that we consistently make medical decisions, such as placing patients on nonbenign antibiotics, on the basis of old studies when we have evidence that should change what we consider to be normal, such as body temperature...


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