COLUMBUS, Ohio -- Taking a newborn's temperature with an infrared thermometer placed under the arm is just as reliable as taking a rectal temperature, new research suggests.
Researchers found that using an infrared thermometer to take the axillary (or underarm) temperature of a newborn baby yielded results very similar to rectal temperature measurements -- at least for babies who were not under a radiant warmer.
"Rectal temperatures have been the gold standard in measuring a newborn's temperature," said John Seguin, associate professor of pediatrics at Ohio State University. "But underarm readings from infrared thermometers can be just as precise and safe and even quicker. It takes less than two seconds to get a result from this type of thermometer."
Nurses usually take an infant's temperature within the first 30 to 60 minutes after birth in order to determine if the infant is too hot or too cold. Fluctuations in temperature could indicate an infection or excessive heat loss, which can cause problems.
The research appears in a recent issue of the journal Clinical Pediatrics.
Seguin and co-author Kimberlee Terry, a former Ohio State medical student, measured the axillary temperatures of 16 newborns using infrared thermometers. They simultaneously compared underarm temperatures to those taken by a rectal thermistor, or plastic-coated wire thermometer.
The researchers took the infants' left and right axillary temperatures when the babies were under a radiant warmer -- much like a heat lamp -- just before the babies' first bath. They again took both underarm temperatures before transferring the babies to the nursery or their mothers' rooms.
The axillary temperatures varied widely when the infants were under the radiant warmers. In fact, 22 percent of the temperatures taken with the infrared thermometer were incorrectly low when compared to the readings of the rectal thermistor.
"There was a greater disagreement between rectal and axillary temperatures in newborn infants under a radiant warmer, which may limit the use of infrared thermometers in this setting," Seguin said.
However, the researchers found that axillary temperatures taken an hour after infants had been wrapped in blankets and placed in cribs were more reliable substitutes for rectal temperature readings.
"Infants tend to move around a lot under the radiant warmer," Seguin said. "The underarm skin temperature may vary, depending on the infant's arm position before the measurement."
The researchers also compared the axillary and rectal temperatures of 12 premature babies in incubators. These babies were studied between five and 51 days of age. The researchers took one axillary reading three hours after a feeding. They found that axillary and rectal temperatures were in close agreement, much like the full-term babies in cribs.
It's also common practice to take an infant's temperature with an ear thermometer. However, the ear canals of newborns are usually too small to yield an accurate reading.
Infrared thermometry -- originally developed by NASA to measure the temperatures of distant stars and planets -- seems to be taking the place of measuring temperatures with electronic thermometers, at least in the hospital setting. Efficiency is a major factor in using infrared thermometers, according to Seguin.
"Mercury thermometers have to be held in place for nearly five minutes, and electronic devices for 90 seconds" he said. "That adds up if a nurse has to take the temperature of 10 or 15 babies several times."
While taking axillary temperatures with an infrared thermometer is a viable option for a newborn in a crib, using these devices on older infants may not yield accurate results.
"They would need to be tested in the older age group," Seguin said. "Researchers in England found that axillary temperatures with mercury-in-glass thermometers were not a good substitute for rectal temperatures in infants up to 6 months old."
The Exergen Corporation of Watertown, Mass., provided the Lightouch Neonate infrared thermometers for this study.