Infrared emission detection (IRED) thermometry of the tympanic membrane is easy and safe. However, studies of the reliability of this method of temperature measurement have provided conflicting information. Smitz and associates compared rectal thermometry to IRED thermometry in elderly hospitalized patients to determine if there was agreement between the temperatures obtained via these two methods.

Fifty hospital patients older than 65 years were included in the study. Patients were excluded if their auditory canals were obstructed with cerumen or if they had contraindications to rectal or ear temperatures. Rectal temperatures were obtained in recumbent patients; temperatures were recorded every two minutes until there had been no change for two minutes. Once the rectal temperature was obtained, a brief otoscopic examination was performed to verify the absence of an occluded auditory canal or the presence of otologic disease. Three IRED measurements were recorded for each ear, with the highest reading being used in the analysis.

Mean rectal temperatures were significantly higher than IRED ear temperatures, although there was a highly significant positive correlation between the two. The mean of the differences between ear and rectal temperatures was 0.5°C (0.9°F). The optimum IRED ear temperature cut-off for diagnosing fever was 37.2°C (99.0°F). Other studies have defined the upper limit for a normal rectal temperature to be 37.5°C (99.5°F).

The authors conclude that IRED ear thermometers can provide accurate information in older hospitalized patients. They point out that these results were obtained using the highest of six IRED ear temperature readings, and that the IRED ear temperature threshold must be specifically defined.

editor's note: This study provides some reassurance that infrared ear temperature devices are reliable in the elderly. However, it must be noted that patients with cerumen in their ears, a common occurrence in the elderly, were excluded. If an infrared ear temperature is to be used to guide therapeutic decisions, it should first be confirmed that the external auditory canals are clear of cerumen.—g.b.h.