Differentiating environmental from disease-related fevers in the term newborn

It is often difficult to differentiate environmental overheating from disease-related fever in the newborn. The purpose of this study was to establish the normal relationship between peripheral skin temperature and rectal temperature in normal newborn infants whose rectal temperatures were in the upper range of normal (99.0 to 99.6 F) and to compare it with that relationship in infants with fevers known to be disease related. Seventy-eight paired rectal and anterior mid-lower leg skin temperatures were obtained from 41 normal 2-day-old infants. Thirteen similar paired temperatures were measured in 13 full-term infants admitted from home with fever (greater than 100.0 F). The rectal temperature-leg temperature (RT-LT) difference in the normal infants ranged between -1 and +4 F, with a mean of +1.14 F, whereas in the febrile infants it ranged between +5.7 and 12.9 F with a mean of 7.90 F. In febrile infants there was no trend in RT-LT difference as rectal temperatures rose whereas normal infants showed a tendency toward a decreasing RT-LT difference with increasing temperatures. When an RT-LT difference of +3 F is chosen as an arbitrary boundary between environmentally overheated infants and infants with disease-related fevers, it is estimated that 0.5% of infants with disease-related fevers would be incorrectly classified. The RT-LT difference adds an objective guideline for evaluation of temperature elevation in the full-term, appropriate for gestational age neonate.