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How to Take Temperature

While taking a temperature is a relatively simple procedure, there are a few key points to keep in mind to ensure that you get the most accurate reading, and best experience from your thermometer.

The first factor to consider when taking a person’s temperature is the measurement site. Typically there are three specific sites that are options for a patient, dependant upon their age and physical condition. For standard stick-type thermometers, you may choose from an oral, axillary, or rectal measurement site.

This chart shows how temperature ranges vary by age and by measurement method. Data from http://www.officialhealth.org/Normal-Body-Temperature.html .
This chart shows how temperature ranges vary by age and by measurement method. Data from http://www.officialhealth.org/Normal-Body-Temperature.html

The primary goal of taking measurements at these sites is to obtain an estimate of a patient’s core body temperature. It is important to note that none of the three methods above actually directly equals a person’s core body temperature. Instead, they represent a measurement that can be compared to the average core temperature. Generally, rectal measurements will be higher, while axillary measurements will be lower.

Average human temperature is approximately 98.6 °F (although this may vary due to a variety of factors). Rectal measurements may be as much as a degree higher, with the average temperature being 99.5 °F. Inversely, axillary measurements tend to be lower, with an average temperature being around 97.7 °F. Even oral temperatures, on average, are lower than core body temperature, with an average reading being 98.2 °F.

Oral Measurement

By far the most popular choice of the three methods, oral measurements can provide accurate and reliable readings and a good representation of core body temperature. This method is generally recommended for patients four years and older who will not bite down on the probe tip during measurement. When taking temperature orally, a few key points to remember include:

  • Drinking or eating very hot or cold food can affect temperature measurement when measuring orally. Advise patients not to eat or drink anything prior to measurement.
  • Physical activity can alter a person’s core body temperature. A patient that has recently exerted themselves should be given time to recuperate prior to taking a measurement.
  • It is important that the patient keep their mouth closed during oral measurements. The ingress of cooler air from the environment can throw off readings. The most accurate results will come when the thermometer is properly positioned in the sublingual pocket and the patient’s mouth is closed.
  • With many thermometer models, it is recommended that you use a probe cover during measurement to keep your thermometer sanitary. Always consult the instructions for use that accompany your thermometer to determine if probe covers are necessary, and what type are required.

Rectal Measurement

  • Generally, water-soluble jelly or petroleum jelly should be used as a lubricant when taking rectal temperatures. This will allow for easier insertion of the probe and increase patient comfort during the measurement. Lubricants are generally placed over the probe cover.
  • The probe tip should be inserted no more than ½ inches or 1.3 cm into the rectum. You should never force the probe tip in if resistance is encountered.
  • It is important to note that a patient who has recently been heavily exercising their legs or lower body may have an elevated rectal temperature.

Axillary Measurement

  • The underarm must be dry prior to measurement. You may need to wipe the patient’s underarm with a dry towel prior to measurement.
  • After placing the probe tip in the armpit, bring the patient’s arm down close against the body to trap body heat.
  • The probe tip should be oriented in the same direction of the body, with the tip towards the patient’s head.

Additional Measurement Sites

The measurement sites described above are the most commonly used, but new technologies allow for alternative measurement sites for those patients who require it, or for convenience. These methods include temporal measurement and tympanic measurement.

New technology, such as a temporal thermometer, simplify taking temperature measurements on pediatric patients.

While these measurement sites require specialized thermometers, they offer more convenient measurements and are ideal for small children that may be more difficult to take measurements on. A key factor with the use of these thermometers is ensuring that the probe is placed properly and that a probe cover is used if one is called for in the instructions for use.

When using an IR ear thermometer or temporal thermometer, always review the provided instructions for use carefully. Note measurement sites, thermometer positioning, and probe cover use carefully prior to taking a measurement. While these methods provide fast temperature measurement, you will have the best results if you observe proper measurement technique. 

As with rectal measurement sites, tympanic (ear) thermometers may give slightly higher readings, and the average temperature is around 99.5 °F. Temporal measurements are closer to true (core) body temperature, and provided that the probe has been properly positioned, will give readings that are closer to average body temperatures of 98.6 °F.