Transcutaneous bilirubin after phototherapy in term and preterm infants.

OBJECTIVES: To compare transcutaneous bilirubin (TcB) readings with total serum bilirubin (TSB) after phototherapy, estimating the range of TcB where confirmation through blood sampling can be avoided.

METHODS: Preterm and term neonates receiving in-hospital phototherapy underwent TcB measurements (device JM-103, TcB) alongside routine TSB before and after treatment. We calculated time-dependent safety margins for transcutaneous readings to correctly assign 99% of infants not to receive phototherapy.

RESULTS: Between August 2011 and December 2012, 86 newborn infants (47 preterm, 39 term) underwent a total of 189 parallel measurements. Mean difference (TcB - TSB) before treatment was -0.6 mg/dL (SD, 1.9 mg/dL). Within the first 8 hours after phototherapy, TcB levels were -2.4 mg/dL (SD, 2.1 mg/dL) below TSB. Thereafter the difference gradually returned to pretreatment values (-1.8 mg/dL in 8-16 hours, -1.1 mg/dL in 16-24 hours, and -0.8 mg/dL after 24 hours), while variations remained stable over time (SD, 1.4-1.8 mg/dL). In the first 8 hours after treatment, TcB levels of -7.3 mg/dL below the individual phototherapy threshold allowed safe rejection of confirmatory blood sampling. After 8 hours, that safety margin was reduced to approximately -5.0 mg/dL.

CONCLUSIONS: TcB measurements remain a valuable tool after phototherapy when time-dependent underestimation of TcB is being accounted for.