I thought the following is kind of interesting. The excerpts are followed by the URLs where the full text can be found. In short, body temperatures not only change thoroughout the day (which we already knew), there is not a good agreement on what correct temperatures should be, or how they are best measured.
Here's the text:
"In 1861, Carl Reinhold August Wunderlich claimed
to measure the temperatures of one million people,
and reported the average to be 37 Ã‚Â°C. In the United
States, normal human body temperature is commonly
quoted as 98.6 Ã‚Â°F, which is an inappropriately exact
conversion of Wunderlich's 19th century announce-
ment that the human body temperature is 37 Ã‚Â°C. In
Russia, the commonly quoted value is 36.6 Ã‚Â°C
(97.9 Ã‚Â°F), based on an armpit reading."
And also this from another URL:
"Normal human body temperature is a concept that
depends upon the place in the body at which the
measurement is made. The value of 36.8 Ã‚Â°C Ã‚Â±0.7 Ã‚Â°C,
or 98.2 Ã‚Â°F Ã‚Â±1.3 Ã‚Â°F is the common oral measurement."
Here is what Broda O. Barnes, MD says in this 1976 book "Hypothyroidism: the Unsuspected Illness":
"...it is worthwhile takig a thermometer to bed with you.
Shake it down well and place it on the night stand.
Immediately upon wakening in the morning, place the
thermometer snugly in the armpit for ten minutes by
the clock. A reading below the normal range of 97.8
to 98.2 strongly suggests low thyroid function. If the
reading is above the normal range, one must be
suspicious of some infection or an overactive thyroid
"The basal temperature is not a perfect test for thyroid
function. There are conditions other than hypothyroidism
that may produce a low reading -- for example,
starvation, pituitary gland deficiency, or adrenal gland
He did not like oral temperatures for several reasons including the possibility of having a sinus infection which would raise the reading, and also, he says such infections are not uncommon with hypothyroidism.
Somewhat ironically, I just took my oral temperature and was pleased to see it at 98.6 for the first time in months (except for right after taking a thyroid pill or two sublingually in recent days). At first it was good news until I remembered that I was thinking a little earlier that I might be coming down with the the flu or a cold (very rare for me). I guess I will know in the morning.
My doctor's suggestion that he looks for 98.6 was probably his way of saying "normal" and making the assumption that I figured, like everyone else, that that is the correct temperature. He could explain further later on about the truth of the situation. That's my best guess for now.
However, another confusing issue is taking the temperature readings in the morning. According to this chart (see URL to follow), highest readings do not occur in the morning, but the afternoon. Maybe we are not after the daily high reading, but rather only the morning reading? So, I am left without answers on the whole deal for now.
I will be better off when I get hold of a mercury thermometer like Barnes used (on "many thousands of people") and do the under arm measurements just has he did so I can use his range. I would not trust my digital thermometer for that as it responds in 10 seconds and the heat transfer from a dry surface (under arm) compared to a wet one (mouth) would not likely cut it.
Anyway, hope I was helpful...
Craig, I am about half-way through the Schwarzbein book. So far mixed reviews particularly regarding her thoughts on diagnoising and treating hypothyroidism and her huge emphasis on serotonin -- both of which are "establishment medicine" ideas. She was trained in endocrinology and appears to paroting the party line on these issues, in my opinion. I like a lot of what she says on other matters though.