Clinical and laboratory thermometers: what is the difference?

Clinical vs laboratory thermometer at a glance

	Clinical thermometer	Laboratory thermometer
Used for	Human body temperature	Water and other things, for example in experiments
What it looks like	A small digital device with a screen	A long, narrow, sealed glass tube with a bulb at one end
How it works	Heat sensors and a battery	A liquid (red-coloured alcohol or mercury) rises or falls in the tube
Range	Made for body temperatures. The human body normally stays between 35 °C and 42 °C	Usually −10 °C to 110 °C
How to read it	Read the number on the screen	Read the mark where the top of the liquid column is
Never hold it by	The tip	The bulb

How do you use a digital clinical thermometer?

1. Read the instruction manual that comes with it.
2. Wash your hands and the tip of the thermometer with soap and water. Keep the display out of the water.
3. Press the reset button.
4. Place the tip under your tongue and close your mouth.
5. Wait until it beeps or a light flashes.
6. Take it out and read the temperature on the display.
7. Wash the tip again, dry it and put the thermometer away.

For small children or old people, the thermometer can be kept in the armpit instead. This reading is about 0.5 °C to 1 °C lower than the actual body temperature, so keep that in mind.

Why are mercury thermometers being replaced?

Earlier, clinical thermometers had mercury inside. Mercury is an extremely toxic substance, and if such a thermometer breaks, the mercury is difficult to dispose of safely. Digital thermometers have no such risk, and their numbers are easier to read. That is why digital thermometers are taking their place.

What is inside a laboratory thermometer?

A laboratory thermometer is a long, narrow, sealed glass tube of the same width all along. At one end is a bulb filled with a liquid, usually alcohol coloured red so that it is easy to see, or mercury. A Celsius scale is marked along the tube. The liquid column rises when the temperature goes up and falls when it goes down, and the mark at the top of the column is the reading.

Handle it with care: it is made of glass and can break if it hits something hard.

Can one thermometer do the other’s job?

• Clinical thermometer for boiling water or ice? No. Their temperatures are far outside the range it is made for.
• Laboratory thermometer for body temperature? No. The column starts falling as soon as the thermometer is taken out of the mouth, so you cannot get a correct reading, and a glass tube with a liquid is not meant to go into the mouth.

What is an infrared thermometer?

During the COVID-19 pandemic, you may have seen people’s temperature being checked from a short distance. Those were non-contact (infrared) thermometers. They measure temperature without touching the body, which lowers the risk of spreading disease.

What is a room thermometer?

The thermometer hung on the wall of a laboratory, clinic or hospital is a room thermometer. It gives an approximate idea of the air temperature in the room. Weather reports use air temperature too: they give the maximum and minimum temperature of each day.