The temperatures measured by several thermometers are different. Do I have a fever?

Winter and spring are the peak seasons for influenza every year. Many people start to worry about whether they have a fever when they have cold symptoms. Therefore, various thermometers at home come in handy - forehead thermometers, ear thermometers, electronic thermometers, and even that "antique" mercury thermometer.

However, the measured temperatures were different: the forehead thermometer showed 36.8℃, the ear thermometer showed 37.5℃, and the mercury thermometer showed 37.2℃... This made people even more confused. Which one was accurate? Did they have a fever?

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01. Why is there a temperature difference between different thermometers?

There are many kinds of thermometers on the market, the commonly used ones are forehead thermometers, ear thermometers, electronic thermometers, and mercury thermometers.

Image source: Photo Network

First of all, different thermometers measure different parts of the body, and the temperature of different parts of the human body is different, so the measured values ​​will also be different . Even if the same person uses a mercury thermometer to measure the left and right armpits at the same time, the results may differ by 0.1-0.2℃, not to mention measuring different parts such as the forehead, ear canal and armpit.

Secondly, the body temperature is not constant. The body temperature of a healthy person is usually between 36-37℃, but there will be slight differences between individuals, and the body temperature will fluctuate with the changes of day and night, gender, activity level, medication, mood and environment . For example, the body temperature in the afternoon is usually slightly higher than that in the morning, and the body temperature will also rise slightly after strenuous exercise, labor or eating, but the fluctuation range will generally not exceed 1℃.

Therefore, it is normal for the temperatures measured by different thermometers to differ.

02. How to choose a thermometer?

Forehead thermometer | Source: Photo Network

1. Forehead thermometer

The forehead thermometer is a non-contact body temperature measuring instrument that measures body temperature by receiving infrared rays emitted by the human forehead. There is no need for direct contact with human skin when using it. Just aim at the position between the eyebrows above the bridge of the nose and press the temperature measurement button. It is simple and fast to operate , and can avoid cross-infection. It is widely used in public places with large traffic such as airports and stations, and can quickly screen out people with abnormal body temperature. However, the measurement results of the forehead thermometer are easily affected by external environmental factors . For example, when the forehead sweats, the ambient temperature is too low or too high, the measurement accuracy may decrease. Once an abnormal body temperature is found, it is necessary to retest.

Recommended users:

Suitable for all people, for use at home or in public places.

Ear thermometer | Source: Photo Network

2. Ear Thermometer

The temperature measurement point of the ear thermometer is the eardrum. Since the temperature of the eardrum is relatively stable and close to the core temperature of the human body, the accuracy of the ear thermometer measurement is relatively high . Before measuring, you need to remove the cerumen (ear wax) in the ear canal, then gently pull the auricle to completely expose the external auditory canal, put the probe into the ear canal and aim it in the direction of the eardrum, press the measurement button, and you can get the measurement data in just a few seconds.

Recommended users:

Suitable for seriously ill patients, the elderly and children, and can be used at home or in hospitals.

Special attention:

It is not recommended to use ear thermometers on babies under 6 months old, because the ear canal needs to be straightened when measuring with an ear thermometer. The baby's ear canal is soft, and improper operation can easily cause invasive damage to the baby.

Electronic thermometer | Source: Photo Network

3. Electronic thermometer

Compared with mercury thermometers, electronic thermometers have won wide popularity for their convenience and safety . Simply place the sensor under the tongue or under the armpit for a few minutes to sense the temperature and convert it into an electrical signal, which can be clearly displayed on the digital display, eliminating the process of reading with a traditional thermometer.

Recommended users:

Suitable for all people.

Mercury-free thermometer | Source: Photo Network

4. Mercury thermometer/mercury-free thermometer

Mercury thermometers use the principle of thermal expansion and contraction of mercury to measure body temperature. Their measurement results are relatively accurate, and they are low-cost and durable . They are often used to measure the temperature of the armpit, mouth or rectum.

However, mercury thermometers are fragile and mercury leakage may lead to mercury poisoning, so a mercury-free thermometer has appeared on the market. It looks similar to a traditional thermometer, but the temperature sensing material is replaced with gallium-indium alloy liquid metal , which is safer than mercury and more expensive. At present, this type of thermometer is commonly used in hospitals.

Recommended users:

It is suitable for people with high cooperation ability who need to accurately obtain the current body temperature. It is usually used at home and in hospitals.

Special attention:

Since this type of thermometer is fragile and takes a long time to measure, it is not recommended to use it for young babies. Once mercury leaks, open the window for ventilation immediately, wear gloves and masks, dip the scattered mercury with a cotton swab, put it in a bottle of water, seal it, and throw it into the hazardous waste bin.

03. How to accurately measure body temperature clinically?

· Axillary measurement: This is a commonly used measurement method in clinical practice, with a normal range of 36.3~37.2°C . Generally, a mercury or mercury-free thermometer can be used for measurement. Place it under the armpit and read the value after 5 minutes. The armpit should be wiped dry before temperature measurement; the upper arm should be clamped during temperature measurement to avoid errors. This method is not suitable for people with armpit trauma or excessive sweating.

Oral measurement method: The normal reference range is 36.5~37.5°C . When measuring, you usually need to sterilize the thermometer and place it under the tongue, close your lips, and keep it for 3~5 minutes before reading the value. It should be noted that infants and people who are unconscious should not use this method to avoid the mercury in the thermometer flowing out of the mouth due to unconscious actions, causing adverse consequences.

· Anal measurement method: The normal reference range is 37~38°C . When measuring, the subject is usually required to lie in a side-lying or prone position, expose the buttocks, lubricate the anal thermometer with soapy water, gently insert the thermometer into the anus 2~3 cm, keep it for 3~5 minutes, and then read the value. This method is not suitable for patients with diarrhea, rectal or anal surgery, so as to avoid measurement errors or irritation of local tissues.

In addition, you can also use an infrared forehead thermometer or ear thermometer for preliminary fever screening, but it is greatly affected by the environment, and factors such as earwax may affect the measurement accuracy. When measuring ear temperature, due to the physiological curvature of the ear canal, the ear canal needs to be straightened to align with the eardrum for measurement.

For children aged six months to one year , the auricle should be gently pulled outward and backward to keep the ear canal as straight as possible; for children over one year old or adults, the auricle should be gently pulled outward and upward to keep the ear canal as straight as possible. When measuring, wait for the ear thermometer to make a "beep" sound to prompt, and read the value. The normal range is usually between 35 and 37°C .

04. How to determine whether you have a fever?

Fever, commonly known as fever, refers to the body temperature rising beyond the normal range under the action of pyrogens or due to various reasons that cause changes in the function of the hypothalamic temperature regulation center. Generally speaking, fever is called fever when the armpit, oral, and rectal temperatures exceed 37°C, 37.3°C, and 37.6°C respectively, or when the temperature fluctuates by more than 1.2°C within 24 hours.

Fever levels are classified based on oral temperature:

① Low fever: body temperature 37.3～38.0℃;

② Moderate fever: body temperature 38.1～39.0℃;

③ High fever: body temperature 39.1～41℃;

④ Hyperthermia: body temperature is above 41°C.

Kind tips:

Eating (such as cold drinks, hot drinks), strenuous exercise, bathing, etc. will affect the measurement results. It is recommended to wait 30 minutes before measuring. The body temperature is only for reference. Whether to take medicine and when to take medicine should be judged comprehensively based on symptoms and personal feelings.

References

[1] Li Xiaohan, Shang Shaomei. Basic Nursing[M]. 6th edition. Beijing: People's Medical Publishing House, 2017.

[2] Ma Dongwei, Zhang Qing, Xu Huijuan, et al. Comparison of various body temperature measurement methods[J]. Metrology and Measurement Technology, 2021, 48(12): 49-51.

[3] Wang Ling, Liu Shuang, Xu Rong. Comparative analysis of measurement results of non-contact infrared forehead thermometer and mercury thermometer[J]. Journal of Nursing, 2021, 36(19): 56-58.

[4] Wan Xuehong, Lu Xuefeng, Liu Chengyu, et al. Diagnostics[M]. 9th edition. Beijing: People's Medical Publishing House, 2018.

Author: Liu Xuling, deputy chief physician of infectious diseases department, Shanghai Pudong District Central Hospital Planning & editing: Tiara Cover image source: Photo Network