The Gold Standard: Rectal Temperature
For infants and toddlers up to age 3, the American Academy of Pediatrics recommends rectal temperature measurement as the most accurate method. A rectal temperature provides the closest reading to a person's true internal core body temperature. While many parents are hesitant, it's often the most crucial method in young children where an accurate fever reading is needed to determine the seriousness of an illness.
How to take a rectal temperature
Taking a rectal temperature requires a dedicated digital thermometer labeled for rectal use. Always follow the manufacturer's instructions, but here are the general steps:
- Use a digital thermometer designed for rectal use. Never use a glass mercury thermometer.
- Clean the thermometer with rubbing alcohol and rinse with lukewarm water, or follow the manufacturer’s cleaning directions.
- Lubricate the tip with petroleum jelly.
- Place the child on their stomach on your lap or a flat surface. Gently separate the buttocks.
- Insert the thermometer tip about 1/2 to 1 inch into the anus. For babies under 6 months, only insert about 1/2 inch.
- Hold the child still and keep the thermometer in place until it beeps.
- Remove and read the temperature. Be sure to note that rectal temps are naturally 0.5°F to 1°F higher than oral temps.
- Clean the thermometer thoroughly after each use and label it clearly to prevent accidental oral use. For detailed, step-by-step instructions on taking a baby's temperature, you can consult resources like Nationwide Children's Hospital's guide.
The Convenient and Accurate Alternative: Forehead (Temporal Artery) Temperature
Forehead thermometers, also known as temporal artery thermometers, use an infrared scanner to measure the temperature of the temporal artery on the forehead. They are very quick, non-invasive, and have gained popularity in clinical settings and homes for their convenience and relative accuracy. They can be used for all ages, including infants, though some research suggests confirmation with a rectal temp may be needed for very young babies.
How to take a forehead temperature
- Turn the thermometer on and ensure the sensor is clean.
- Place the sensor in the center of the forehead, touching the skin.
- Press and hold the scan button while slowly sliding the thermometer across the forehead toward the top of the ear until it beeps.
- For non-contact versions, hold the device at the manufacturer's recommended distance from the forehead.
- External factors like sweating or cold environments can affect the reading, so ensure the forehead is clean and dry.
The Common Method: Oral Temperature
For children over 4 years of age and adults who can hold a thermometer properly under their tongue, oral temperature is a safe and reliable method. While convenient, its accuracy can be impacted by external factors. To get the best reading, you must wait at least 30 minutes after eating, drinking, or smoking.
How to take an oral temperature
- Turn on a digital thermometer.
- Place the tip of the probe under the tongue, toward the back of the mouth in one of the pockets next to the frenulum.
- Close the lips around the thermometer to hold it in place. Do not bite down.
- Wait for the thermometer to beep, indicating the reading is complete.
The Fast but Fickle Method: Ear (Tympanic) Temperature
Ear thermometers use infrared technology to measure the heat from the eardrum and are suitable for children over 6 months old and adults. While fast, they are often less reliable than other methods due to the need for correct placement within the ear canal and potential blockage from earwax.
How to take an ear temperature
- Turn on the ear thermometer.
- Gently pull the ear back and up (for children over 1 year) to straighten the ear canal.
- Insert the thermometer into the ear canal and aim it at the eardrum.
- Press the button and wait for the beep.
The Least Accurate: Armpit (Axillary) Temperature
Taking a temperature under the armpit is the least accurate method, often used as an initial screening tool rather than for definitive fever diagnosis. If a fever is detected via the axillary method, it should be confirmed with a more accurate method, such as rectal or forehead temperature.
How to take an armpit temperature
- Turn on a digital thermometer.
- Place the tip of the probe in the center of a dry armpit.
- Hold the arm tightly against the chest to keep the thermometer in place until it beeps.
Comparison of Thermometer Methods
| Method | Relative Accuracy | Age Suitability | Speed | Invasiveness |
|---|---|---|---|---|
| Rectal | Highest (Core Temp) | Infants & Toddlers (<3 yrs) | Fast | High |
| Forehead (Temporal) | High | All Ages | Very Fast | Low |
| Oral | Moderate to High | Children (>4 yrs) & Adults | Moderate | Moderate |
| Ear (Tympanic) | Moderate (User Dependent) | Children (>6 mos) & Adults | Very Fast | Low |
| Armpit (Axillary) | Low (Screening Only) | All Ages | Slow | Very Low |
Factors Affecting Accuracy
Beyond the choice of site, several factors can influence the accuracy of a temperature reading:
- Proper Technique: Failure to follow the manufacturer's directions can lead to inaccurate results. This is particularly relevant for ear thermometers, where correct placement is essential.
- External Conditions: Environmental factors, such as ambient temperature, can impact non-contact methods. For example, a cold forehead can lead to a lower temporal reading.
- Device Quality: The quality of the thermometer itself, from manufacturing to proper calibration, plays a significant role in its reliability over time. Higher-end models may offer more consistent readings.
- Other Factors: For oral readings, recent consumption of hot or cold beverages can skew results. For ear readings, excessive earwax can cause interference.
Conclusion
For the most accurate body temperature reading, the rectal method is the undisputed gold standard, particularly for young children and infants. For a highly accurate yet less invasive option suitable for all ages, a temporal artery (forehead) thermometer is an excellent choice. When convenience is a priority for older children and adults, oral temperature is reliable if performed correctly. Understanding the strengths and weaknesses of each method allows for better health monitoring and more informed decisions about when to seek medical attention.
