Accuracy in Glass and Digital Thermometers

Digital Thermometers

Are digital thermometers more accurate? Accuracy in determining body temperature depends on many factors.

Almost all the common medical devices have become digital these days, and thermometers are no exception, but does being digital mean being more accurate? It is safe to say that many people still use mercury-in-glass or alcohol thermometers and there are those who are a little skeptical of the digital devices! However, whether using mercury or digital thermometers, accurate measurement of body temperature, has its own rules and fever detection depends on different hours of the day.


Types of medical thermometers

Medical thermometers are divided into different types of glass, strip, ear, rectal, and digital thermometers. Glass thermometers consist of two parts: a metal part, which usually contacts the surface of the mucosa or other holes in the body, and a glass part that contains colored alcohol or mercury. The metal part transfers heat to the liquid inside the glass, and the expansion and contraction of that liquid shows us the temperature. Depending on the area ​​in which the thermometer is used, its appearance may vary. The oral type, commonly used in most hospitals and clinics, has a metal tip of about one centimeter, which usually enters the oral cavity beneath the tongue. When placed under the tongue, the mouth should be completely closed, but the teeth should not be pressed. Otherwise the glass container may break. Simply place it between the lips for at least one to three minutes so that the metal part is under the tongue. Then by removing the thermometer, the number that indicates the level of mercury or alcohol is the actual or central body temperature.


What should be taken into account for an accurate body temperature measurement?

Regardless of whether you are using glass or digital thermometers, it is important to know that sometimes the temperature of the skin surface or the mucosa surface may change for some reason. For example, vigorous exercise or drinking hot liquids makes the mucus surface slightly warmer. In such circumstances the thermometer does not show the actual temperature. So remember not to drink hot liquids or do heavy exercise before measuring your body temperature.


Glass Thermometers

Why should we add half a degree to the axillary (armpit) temperature?

Sometimes it is not possible to measure the body temperature through the oral cavity. For example, patients admitted to the ICU, those with seizures who may break the thermometer, those with a conscious impairment who cannot hold the thermometer in their mouth, or those who have respiratory problems cannot use an oral thermometers. In such cases, the metal part of the oral thermometer can be placed in the densest area of ​​the armpit for at least three minutes, with the arm fully attached to the body and then read the temperature. What is important in this measurement is that the underarm temperature is the surface temperature of the skin and does not reflect the central body temperature as the mucosal temperature does. For this reason, one must add half a degree to the degree of temperature read from the armpit to achieve true body temperature.


For children only

Another type of glass thermometer is the rectal type, which is often used for infants and toddlers because infants and children cannot co-operate and cannot hold the thermometer in their mouths. The rectal thermometer usually has a prominent, very small tip that is inserted about two centimeters into the baby’s anus for one to three minutes. Then it is taken out and read like a glass thermometer. Rectal thermometer makes the most accurate measurement though it may sometimes show temperatures half as high as the actual body temperature. Since it is a little difficult to use and may be embarrassing or even painful to the patient, this type of measurement is preferable only to children.


Strip thermometers are not accurate

The headband thermometers are a simpler type of thermometer and are more suitable for those who cannot read the mercury level. In fact, these thermometers show the temperature number when the forehead, but usually not the central body temperature because the forehead is the outermost area of the body and the skin cannot show the actual body temperature. Therefore, this thermometer does not make accurate measurements. However, it is recommended that if you use it, add half the temperature to the measured temperature to get closer to the central body temperature.


Digital thermometers are faster and easier to read


A thermometer for those who are in a rush

Another type of thermometer is the ear type that is inserted in the ear canal. This electronic thermometer is used in pediatricians and is not usually used by adults. The newest type of ear thermometer is the digital one. This thermometer has a digital plate instead of a glass or mercury chamber that displays the temperature on the digital plate after contact with the metal body. The advantage of this thermometer is that it is faster. You no longer have to wait three minutes. These devices usually beep very fast in half a minute and display the temperature.



How accurate are digital thermometers compared to glass thermometers?

The accuracy of digital thermometers is almost identical to that of mercury or alcohol thermometers. In fact, their digital screen does the same thing as mercury or alcohol, and the only difference is that it shows the temperature number digitally on its own, so it’s easier to read. When you try to read the level of mercury or alcohol, you may not have accuracy in reading the degree on the thermometer. So digital thermometers can be more precise in this respect. Another advantage of digital thermometers is that they are faster, but both thermometers can be precise or half a degree lower or higher than the central temperature depending on where they are used (mouth, armpit, anus, etc.).


Body temperature also depends on the time of the day

Overall normal body temperature varies from 36 to 37.5 degrees depending on what time of the day it is, and higher (fever) or too lower (hypothermia) degrees can be dangerous. The highest temperature in the day occurs usually from afternoon to the evening between 3-8 p.m. Up to 37.5 is considered normal at this time. The lowest temperature is usually in the morning when you wake up, which is between 36 to 36.5 degrees at this time. So normal body temperature depends on daytime conditions. For example, a temperature of 37.5 degrees in the morning can be a fever, but the same temperature between afternoon and evening is considered to be normal.

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