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.


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.


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.


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

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