Comparison of rectal, axillary, and forehead temperatures

Abstract

Objective: To assess whether axillary and forehead temperatures accurately reflect the rectal temperature (the criterion standard)

Design: Prospective study with calculation of paired axillary-rectal and forehead-rectal temperature differences and their SDs.

Setting: Referral hospital.

Participants: Convenience sample of 120 patients, with 20 patients in each of six age groups (ie, < 1 month, 1 to 5 months, 6 to 11 months, 12 to 23 months, 2 to 14 years, and adults)

Results: In newborns, the rectal temperature was equal to the axillary temperature plus 0.2 degrees C for each week of age up to 5 weeks; forehead strip thermometers gave inaccurate readings in this age group. In patients older than 1 month, the mean difference (SD) between the rectal and axillary temperatures was 1.04 degrees C (0.45 degrees C); thus the axillary temperature was adjusted by adding 1 degree C, and no adjusted axillary temperature differed from the rectal temperature by more than 1 degree C. The mean difference (SD) between the forehead temperature that was measured by the best forehead liquid crystal strip thermometer (FeverScan) and the rectal temperature was 0.14 degrees C (0.60 degrees C); 10 forehead temperatures differed from the rectal temperature by more than 1 degree C.

Conclusions: Previous studies that have suggested that axillary and forehead temperatures do not provide a reliable guide to the rectal temperature have all used inappropriate methods of analysis (correlation coefficients or sensitivity and specificity); previous studies that have based their conclusions on the correct method of analysis (paired differences and their SDs) have all found that the axillary temperature gives a good indication of the rectal temperature. The axillary temperature can be measured safely at any age, and the axillary temperature plus 1 degree C is a good guide to the rectal temperature in patients older than 1 month. Forehead strip thermometers are easy to use, but they do not estimate the rectal temperature as accurately as the axillary temperature does.