Monitoring body temperature is essential for assessing health, as fever often indicates illness. Obtaining an accurate reading depends entirely on selecting the correct measurement location and executing the technique precisely. Different body sites provide varying estimates of internal temperature, meaning thermometer placement directly influences the result. Understanding these site-specific requirements is necessary for interpreting the measurement reliably.
Oral and Rectal Placement Techniques
Rectal Measurement
The rectal method is the most accurate way to measure temperature, especially in infants and young children up to three years old, because it closely reflects core body temperature. The thermometer tip should be covered with a water-soluble lubricant and gently inserted into the rectum. Insertion depth is about one-half inch for infants younger than six months, and up to one inch for older children. The device must be held in place until the reading is complete.
Oral Measurement
Oral measurement is common for cooperative individuals, generally those over four years old. The probe tip must be placed deep into the sublingual pocket beneath the tongue toward the back of the mouth. The person should close their lips around the thermometer, keeping the mouth sealed and breathing through the nose to prevent ambient air from skewing the result. Wait at least 15 minutes after consuming hot or cold food or drink, as this can temporarily alter the mouth’s surface temperature.
Axillary Placement and Accuracy
The axillary (armpit) method is used when oral or rectal measurements are impractical. The armpit must be completely dry before measurement, as moisture can lower the reading due to evaporative cooling. The thermometer tip should be positioned high in the center of the armpit, resting directly against the skin over the axillary artery. The patient’s arm must be held snugly against the chest to trap heat and ensure full contact with the probe.
Axillary measurement is considered the least accurate method because it measures skin surface temperature rather than internal body temperature. It is best suited for initial fever screening rather than providing a definitive reading. Although waiting until the thermometer beeps is necessary, the result may require an upward adjustment to estimate core temperature.
Forehead and Ear Scanning Techniques
Infrared thermometers, including temporal artery (forehead) and tympanic (ear) scanners, offer rapid, minimally invasive options. Temporal artery thermometers measure heat radiating from the artery just beneath the skin of the forehead. The technique involves placing the scanner in the center of the forehead and gently sliding it across the skin to the hairline, maintaining continuous contact.
This method is sensitive to environmental factors; sweat can lower the reading, while wearing a hat can increase it. Tympanic thermometers measure infrared energy emitted from the eardrum, which is a good proxy for core body temperature. To obtain an accurate tympanic reading, the ear canal must be straightened by gently pulling the outer ear up and back before inserting the probe. Excessive earwax or an ear infection can significantly interfere with accuracy.
Selecting the Appropriate Measurement Site
The choice of measurement site is guided primarily by the patient’s age and ability to cooperate. Rectal temperature is the recommended standard for infants up to three months old due to its superior accuracy. For children between three months and four years, temporal artery or tympanic measurement offers a less invasive alternative, though a rectal reading may be necessary to confirm a high temperature.
Oral measurement is suitable only for children older than four years and adults who can reliably hold the thermometer in the correct position with their mouth closed. The oral method should be avoided if a patient is uncooperative, experiencing seizures, or has nasal congestion that forces mouth breathing. The axillary method serves as a simple screening tool when other methods are difficult.
Reading Adjustments by Location
A measurement must be interpreted with the understanding that a normal temperature varies depending on the location taken. Rectal and tympanic (ear) readings are generally 0.5 to 1.0 degrees Fahrenheit higher than an oral reading. Conversely, readings taken from the armpit or temporal artery tend to be lower than an oral temperature, often by the same margin.
This variation means a temperature registering as a fever in one location may be considered normal at another site. Therefore, when communicating a temperature to a healthcare professional, it is necessary to state both the numerical value and the exact location where the measurement was taken.