'Silent' pyrexia in the elderly.

Simultaneous oral, rectal and axillary temperatures were measured in 73 elderly patients on a geriatric unit. Axillary and oral temperatures were significantly lower than rectal readings. If oral or axillary temperatures alone had been measured, pyrexia would have been missed in two thirds of patients with a rectal temperature of 37.5 degrees C or more, and about three quarters of those with a rectal temperature of 38 degrees C or more. These findings suggest that oral or axillary temperature measurements are inadequate screening tests for pyrexia in the elderly.