Initial response of serum bilirubin levels to phototherapy.

We demonstrated the phenomenon of transiently increasing total serum bilirubin within 4 h of phototherapy. We attempted to resolve the mechanism of this phenomenon in 29 hyperbilirubinemic full-term newborn infants who received continuous phototherapy for 24 h. Our present study suggests that this phenomenon may in part be bilirubin load (photobilirubin, photoisomers) from skin and subcutaneous bilirubin and/or peripheral capillary wall bilirubin into the blood stream pool, rather than delayed clearance of bilirubin and photoisomers from the blood stream to bile or urine. Further study is needed to determine these bilirubin compounds for safe and more effective phototherapy.