Transcutaneous bilirubinometry II. Dermal bilirubin kinetics during phototherapy.

We examined the effect of phototherapy on cutaneous bilirubin using the transcutaneous bilirubinometer (TcB) in 14 white infants at a mean postnatal age of 30 h. Six infants were treated with blue light, eight with white light. An opaque patch, 2.5 cm in diameter, covered the skin and served as a source for TcB control values. Simultaneous TcB measurements were obtained from exposed and patched areas every 15 min during 4 h of phototherapy. After the start of phototherapy, TcB index obtained from patched skin did not change during the course of treatment. Data from exposed skin showed that the initial rate of TcB index fall during the first hour was significantly faster than the successive values during the next 3 h in both groups studied. During the first 2 h of therapy the TcB index decreased faster among infants treated with blue light. Correlation studies indicate that TcB measurements from exposed skin areas may not be clinically useful in predicting serum bilirubin response to phototherapy but data obtained from unexposed sites may fill this role.