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Temperature measurement

The measurement of body temperature can help detect illness. It can also monitor whether or not treatment is working. A high temperature is a fever.

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Temperature measurement

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How the Test is Performed

The American Academy of Pediatrics (AAP) recommends not to use glass thermometers with mercury. The glass can break, and mercury is a poison.

Electronic thermometers are most often suggested. An easy-to-read panel shows the temperature. The probe can be placed in the mouth, rectum, or armpit.

Plastic strip thermometers change color to show the temperature. This method is the least accurate.

Electronic ear thermometers are common. They are easy to use. However, some users report that the results are less accurate than with probe thermometers.

Electronic forehead thermometers are more accurate than ear thermometers and their accuracy is similar to probe thermometers.

How to Prepare for the Test

Always clean the thermometer before and after using. You can use cool, soapy water or rubbing alcohol.

Wait at least 1 hour after heavy exercise or a hot bath before measuring body temperature. Wait for 20 to 30 minutes after smoking, eating, or drinking a hot or cold liquid.

Normal Results

The average normal body temperature is 98.6°F (37°C). The normal temperature can vary due to things such as:

You need to have an accurate temperature measurement to determine if a fever is present. Be sure to tell your health care provider which type of temperature measurement you used when discussing a fever.

The exact relationship between different types of temperature measurement is unclear. However, the following general guidelines for temperature results are used:

The average normal oral temperature is 98.6°F (37°C).

Other factors to take into account are:

What Abnormal Results Mean

If the reading on the thermometer is more than 1 to 1.5 degrees above your normal temperature, you have a fever. Fevers may be a sign of:

Body temperature can also be raised by:

Body temperature that is too high or too low can be serious. Contact your provider if this is the case.

Related topics include:

Related Information

Fever

References

McGrath JL, Bachmann DJ. Vital signs measurement. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges' Clinical Procedures in Emergency Medicine and Acute Care. 7th ed. Philadelphia, PA: Elsevier; 2019:chap 1.

Sajadi MM, Romanovsky AA. Temperature regulation and the pathogenesis of fever. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 55.

Ward MA, Hannemann NL. Fever: pathogenesis and treatment. In: Cherry JD, Harrison GJ, Kaplan SL, Steinbach WJ, Hotez PJ, eds. Feigin and Cherry's Textbook of Pediatric Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier; 2019:chap 4.

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Review Date: 1/29/2022  

Reviewed By: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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