Rectal-axillary temperature difference in febrile and afebrile infants and children

The rectal-axillary temperature difference (R-A) was measured in the morning, at midday, and in the afternoon on 1,519 occasions in 1,149 children from birth to 5 years old. Of these, 302 children were febrile (rectal temperature > or = 38 degrees C) and 847 were afebrile. A wide range in R-A was found for each individual in both groups. The magnitude of this difference was not associated with sex or age. In febrile children, the R-A was significantly greater (P < .0001) at the apparent onset of fever (1.04 +/- 0.25 degrees C) than later, when fever had been present for at least two hours (0.53 +/- 0.22 degrees C). These findings indicate that it is impossible to find a standard number by which to convert axillary to rectal temperature or vice versa. Furthermore axillary temperature may be relatively low or even "normal" despite an elevated rectal temperature at the onset of fever.