When an infant seems unwell, obtaining an accurate temperature reading is necessary for determining the appropriate course of action. For babies from birth to three years of age, the rectal method is widely regarded by pediatricians as the most reliable way to measure core body temperature. Other methods, such as armpit or forehead scans, are less precise and may not capture the rapid temperature fluctuations common in young infants. Using the rectal method provides the accurate data needed for immediate decisions, especially since newborns and very young babies can quickly become seriously ill.
Essential Preparation and Supplies
Before attempting to take a rectal temperature, gathering all necessary equipment ensures a fast and smooth procedure. You must use a digital stick thermometer, and it should be clearly labeled for rectal use only to prevent cross-contamination with an oral thermometer. Never use a glass or mercury thermometer, as they pose a safety risk if they break.
The tip of the thermometer should be lubricated with a small amount of petroleum jelly or another water-soluble lubricant to ensure comfortable insertion. Prepare a clean, flat, and stable surface for the baby, such as a changing table or the parent’s lap. Having everything ready minimizes the time the baby is exposed and uncomfortable, which helps keep them calm.
Step-by-Step Guide for Rectal Temperature
The procedure begins with positioning the baby securely to prevent sudden movements that could cause injury. A common position is laying the baby face-up with their legs bent and lifted toward their chest. Alternatively, place the baby belly-down across your lap or a firm surface; if belly-down, placing one hand on their lower back helps keep them still.
Insertion and Stabilization
Once the digital thermometer is lubricated and turned on, gently insert the tip into the anal opening. The recommended insertion depth is approximately 1/2 inch to 1 inch, or just until the silver tip is no longer visible. Angle the tip slightly toward the baby’s belly button for the best access.
As you insert the thermometer, cup your hand against the baby’s bottom, steadying the device between your second and third fingers. This grip stabilizes the thermometer and allows your hand to move with the baby, preventing accidental deep insertion. You must hold the thermometer for the entire reading time and never let go or leave the baby unattended.
Wait until the thermometer beeps or signals that the reading is complete, which typically takes only a few seconds. After the signal, carefully remove the thermometer and read the temperature displayed on the screen. The entire process should be done calmly and quickly; if you encounter any resistance during insertion, remove the thermometer immediately and do not attempt to force it.
What the Numbers Mean
The threshold that defines a fever in an infant using the rectal method is 100.4°F (38°C) or higher, which warrants immediate attention. The average normal rectal temperature for a baby is approximately 98.6°F (37°C). This temperature can fluctuate naturally throughout the day, ranging from a low of 96.8°F to a high of 100.3°F.
A rectal temperature reading is typically about one degree Fahrenheit higher than an armpit temperature, which is why the rectal measurement is preferred for diagnostic accuracy in infants. A temperature at or above 100.4°F signifies that the body’s natural immune response has been activated.
A reading of 100.4°F or above in a young infant requires contacting a medical professional. For babies under three months of age, this number requires prompt medical evaluation regardless of how the infant appears. Parents should record the specific temperature and the time it was taken, as this information is crucial for the healthcare provider.
Safety Considerations and When to Call the Doctor
After each use, the thermometer must be thoroughly cleaned with soap and cool water, or wiped down with rubbing alcohol, to prevent the spread of germs. The thermometer should then be stored safely and kept separate from any oral thermometers. Avoid taking a rectal temperature if the baby has severe diarrhea or visible irritation or bleeding around the anus.
If a baby under three months old has a rectal temperature of 100.4°F (38°C) or higher, medical attention should be sought immediately, often by going to an emergency department. Even if the temperature is below the fever threshold, you must call the doctor if the baby exhibits concerning symptoms.
Professional medical advice is warranted if the baby looks or acts very sick, or if a fever persists beyond 24 hours in a child under two years old. You should also call the doctor if the baby exhibits any of the following warning signs:
- A baby who is inconsolable, difficult to wake up, or unusually drowsy.
- Difficulty breathing.
- A stiff neck.
- A sunken soft spot on the head.
- Any signs of dehydration, such as fewer wet diapers.