Now that you are an expert about the biochemical reasons for fever and the definition of “true” fever (if you missed the first installment of The Fever Files you can click here), let’s talk shopping…for thermometers that is.
When it comes to thermometers, the options available on the market today far exceed the simple glass enclosed mercury thermometers that you had to “shake down” which were the only option about 20 years ago. In fact, you will probably be hard pressed to find a mercury thermometer on market shelves today as there is a risk for the glass breaking with subsequent release of mercury vapors. So with all of the choices available, what type of thermometer is really best? First, let’s discuss the various kinds of thermometers out there.
Digital Thermometers - The small silver tip on the bottom of these thermometers contain an electric heat sensor that can measure body temperature either under the tongue (oral), in the armpit (axillary), or inserted into the bottom (rectal). Purchasing plastic thermometer sheath covers means that these digital thermometers can be used interchangeably in all 3 locations. If not using these plastic sheaths, I would recommend having one thermometer for oral/axillary use and one for rectal use as no one wants to confuse the oral and rectal thermometer! The age of the child will often determine in which location the temperature should be taken. I typically recommend that if your child is under 2 years of age, the rectal method is going to be best and most accurate. Typically, by 3-4 years of age, children can be cooperative enough (or you can at least get them to play a “game”) to hold a thermometer under their tongue so that an oral temperature can be obtained.
Axillary is probably my least desired method of taking a temperature, regardless of a child’s age, because it can be difficult to know what to do with these temperature readings. Do you add a degree? That is a great question. I do not know of any scientific study proving that axillary temperatures are exactly 1 degree less than the actual body temperature. And that one degree can make a HUGE difference especially in infants under 2 months of age.
Digital Tympanic Thermometers - These thermometers read the infrared heat waves produced by the ear membrane. While it sounds like a simple enough task to obtain a temperature from the ear, these devices (and the kiddos you use them on) can be a little tricky. The tip of the thermometer needs to have the proper placement and fit in the ear in order to be accurate. More curved ear canals and those canals that have a lot of wax (which, let’s face it, is a lot of kiddos) can cause incorrect readings. And with a lot of kids, like my wonderful daughter, getting anything into or around their ears is like trying to get them to eat brussel sprouts…it just ain’t happenin’. And while we’re on the topic, keep in mind that tympanic thermometers are not recommended for kids under 6 months of age because of inaccuracies.
Digital Temporal Artery Thermometers - The temporal artery runs across the forehead, and these thermometers use infrared sensors to measure the heat released from this artery. While several studies have shown these to be quite accurate with results back within a few seconds, there are several factors that can affect their accuracy including sweating (since sweat cools the skin the reading will be lower than actual temperature), measuring on the side of the head that a child has been sleeping on (will be much warmer than the other side), and wiggly children (the sensor needs to stay in contact with the head to be as accurate as possible). One major plus with these though…you can use them on a sleeping child. But, once again, if you get a very abnormal reading especially in a child under 2 years of age, their temperature should be verified with a rectal thermometer.
So in the end, I think it is a must for your home medicine bag to have a good ‘ole digital thermometer with plastic covers. If you are looking to purchase one of the more non-invasive thermometers, a review of recent medical literature indicates that the temporal artery scanners are closer to true core temperature (i.e. rectal temperature) when compared to the readings from tympanic thermometers. Remember though, any measurement of temperature in infants and young children that is obtained other than rectally, should really be considered a “screening temperature.”
So, now you understand the science of fever and you are equipped with the perfect thermometer. Next up…we will discuss when fever is an emergency so stay tuned!