Introduction There is insufficient evidence to determine if non-invasive transcutaneous bilirubin (TcB) measurement can replace serum bilirubin (SBR) in assessing rebound hyperbilirubinaemia after phototherapy.

Objective To investigate if TcB can safely guide management of neonates after phototherapy.

Subjects 100 well neonates ≥35 weeks’ gestation who had received inpatient phototherapy.

Method Measurement of both helix (manufacturer’s recommendation) and earlobe TcB coincidentally with routine SBR 12 hours after cessation of phototherapy. All mothers gave written informed consent.

Results Gestation ranged from 35⁺⁰ to 41⁺⁵ (median 37⁺⁶) weeks; birth weight 2018–4566 (median 3230) g; age 55–222 (median 109) hours at testing. 86% neonates were Caucasian. Outcomes determined by SBR included restarting phototherapy (n=0), repeat SBR next day (n=29), no further routine follow-up (n=71).

TcB and SBR measurements were unpredictably inconsistent. Helix TcB tended to underestimate SBR (mean difference 50.1 (95% CI 113.9 to -13.7) μmols/L); for earlobe TcB mean difference was -13.4 (95% CI 46.3 to -73.2) μmols/L (overestimate), but bias was greater over the range of mean differences. No demographic factor predicted consistency between TcB and SBR. TcB was 25% (helix) and 76% (earlobe) sensitive in predicting repeat phototherapy and/or repeat SBR; specificities were 92% and 58%, respectively. Adding a safety margin of 120 μmols/L to helix TcB value could have safely avoided invasive SBR measurement in 50/98 (51%) babies.

Conclusions Consistency between TcB and rebound SBR is unpredictable in well neonates >35 weeks’ gestation but adopting a wide safety margin has potential to reduce blood sampling. Recommencement of phototherapy is uncommon in this population.