Thermometers are Inherently Inaccurate, and That's OK

Thermometers are Inherently Inaccurate, 
and That's OK

One of the most common questions we get asked is what thermometer do we recommend, and questions related to temperatures taken.  Is an ear thermometer better than an axillary thermometer?  Do you add a degree if you take it axillary (under the arm)?

Some background on fever
These questions all have to do with the question of fever itself.  At the heart of the concern of fever is the very real worry, how will I know if this illness is going to be dangerous or mild?  Fever turns out to be a bad guide.   How is that possible?  Just think, someone can have a very mild illness, a harmless cold, but still have a fever of 105.8, or someone could have a very dangerous infection such as a meningitis, and only have a fever of 101.  The height of the temperature does not indicate the seriousness of the infection.

So when we hear your child has a fever, we think, the fever means an infection is present, now let's determine if it is a mild or serious infection.  Mild by the way means that the infection poses no harm and once gone will leave no trace, not that your child will feel good while they have the mild infection.  In fact, most mild infections, like colds, flus, and stomach flus, cause tremendous discomfort, but they don't cause any lasting harm.   So even though the discomfort is not mild, the danger is very mild, because there is no real danger in such infections, as long as they do not change into more serious conditions, of course.

What is normal temperature inside the body?
So with the fact that the temperature, as long as it remains at 105.8 or below, is not an issue of concern by itself, in mind, let's take a look at how thermometers used in our homes work, or don't.

The real definition of fever by the way, is an elevation in core, not skin temperature.  The core temperature is very close to constant if no fever is present.  Across all humanity, the average core temperature is 98.6 degrees Fahrenheit (or 37 degrees Celsius).  This is an average, normal temperature for an individual ranges from about 97 to about 99 or even 100.  That range is a range across all people measured.  For any one person, their normal temperature is a number in that range, with some, but not much variation from time to time.  Again, these numbers describe the actual temperature of organs inside your body, like your blood, lungs, kidneys, etc.

The temperature of our skin varies quite a bit as part of our body's mechanism to keep our inner core temperature as constant as possible.  If our inner body temperature is dropping, the skin diverts blood flow away from the skin to preserve heat, this causes the skin to get cold.  This is experienced by anyone outdoors for some time in the cold, or if a fever is going up and is experienced as feeling chilled.  If the body's inner temperature is too warm, the skin boosts blood flow causing it to flush and feel warm.

But the temperature that counts is the actual temperature of the inside of the body, the temperature of the organs all of which only function well in a very narrow range of temperatures, really about 96-105.8, and typically around 97-99.

How do the thermometers in use perform?
About 40 or more years ago, the standard thermometer parents used was the rectal thermometer, and it gives a pretty accurate read of the actual temperature of the inside of the body.

But no one uses this technique routinely anymore.  The new thermometers are ear, axillary, and infrared thermometers.  All of these thermometers measure skin temperature, and as we just discussed, the skin and inner temperature often vary.

One recent study found they vary quite a bit:

This study looked at 75 publications with about 8,600 patients tested.  They found that if a surface thermometer (ear, axillary, or infrared) found an elevated temperature, the child had a 96% percent chance of having a truly elevated inner or core temperature.   So a temperature over 100.4 by any thermometer in common use almost certainly means your child has a fever for real.

The surface thermometers were fairly inaccurate with common levels of error hovering around 1/2 to 3 full degrees Fahrenheit.  So the actual number on your thermometer is not nearly as important as whether it is over 100.4.

1.  Fever is not as important as how your child is doing to determine if the illness present is mild or serious.  (See post from 2011 below).  Therefore, the number of the thermometer is not that important.
2.  What is important is whether your child with a fever is having trouble breathing, in significant pain, or has a stiff neck.   If none of these symptoms are present and they seem comfortable, a serious infection is much less likely.
3.  Therefore, taking a temperature is not a very helpful indicator of how sick your child is.  A rise in temperature is related, however, to how uncomfortable one is.
4.  The relative unimportance of the temperature is good news given how unreliable the read of the temperature is on the surface in relation to the inner or core temperature.  Whether using ear, axillary, or infrared technology, you are getting mainly surface temperatures which vary from 1/2-3 degrees Fahrenheit off the actual core temperature.
5.  But, if your thermometer registers a temperature of 100.4 or higher, it is almost certain a fever is present.
6.  If you do take a temperature and report it to us, just tell us the number the thermometer gave you and how you took it.  There is no value in adding a degree or subtracting a degree for various techniques.
7.  Put it all together and we have that taking a temperature is not very important, it often bears little relation to the actual inner temperature.  This is fine because of much more value is knowing if your child has symptoms of more severe illness, such as trouble breathing, stiff neck, or significant pain.

To Your Health,
Dr. Lavin 

*Disclaimer* The comments contained in this electronic source of information do not constitute and are not designed to imply that they constitute any form of individual medical advice. The information provided is purely for informational purposes only and not relevant to any person's particular medical condition or situation. If you have any medical concerns about yourself or your family please contact your physician immediately. In order to provide our patients the best uninfluenced information that science has to offer,we do not accept samples of drugs, advertising tchotchkes, money, food, or any item from outside vendors.

 Reminder that Fever is Harmless (Posted March, 2011)

Advanced Pediatrics was very pleased to be contacted by a reporter from Suite 101.com to discuss the recent American Academy of Pediatrics (AAP) campaign to remind families that fever is not a harmful symptom.

Suite 101.com is rated as one of the top 10 blog spots and receives 28 million hits a month, so we were especially pleased that we could get our message out to over 300 million people a year.

Here is our interview, we hope you find it informative and helpful.

Our key points are:
  • Fever remains a fearsome symptom for two key reasons:
  1. For most of human history, infections were the number one cause of death in childhood, causing as many as one in four children to pass.
  2. Even today, fever makes everyone feel terrible.
  • Fever today should no longer create fear for two key reasons:
  1. In the US and the rest of the developed world, death from infection is now very, very rare in childhood.  Fever no longer indicates a likely hazard.
  2. Fever, although uncomforrable, is not dangerous.  Everyone gets fevers, everyone.  With almost no exceptions, fever itself causes no actual harm.
  • More important to be concerned about than fever are signs of serious infection:  Stiff neck, trouble getting air in and out of the chest, severe pain, worrisome rashes.

Dr. Arthur Lavin 

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