Usefulness of transcutaneous bilirubin assessment measured in non-photo-exposed skin to guide the length of phototherapy: an observational study.

Background Transcutaneous bilirubinometers are a non-invasive tool to estimate serum bilirubin. However, once on phototherapy (PHT) and after PHT, its usefulness is precluded. The objective of this study was to prove the hypothesis that transcutaneous bilirubin (TcB) assessment in a covered skin area during PHT could be used to guide the duration of PHT in term and moderate-late preterm infants with non-isoimmune hyperbilirubinemia. Methods A small area of parasternal skin was covered before starting on PHT. Total serum and TcB (both in exposed and non-exposed areas) were determined before starting treatment, every 12 h once on PHT and 12 h after its discontinuation. Pearson's correlation coefficient and paired mean differences between TcB and total serum bilirubin (TSB) were calculated. Bland-Altman plots were obtained. The percentage of correct treatment decisions made based on non-exposed TcB values was calculated. Results During PHT, there was a relatively good correlation between TSB and non-exposed TcB (0.74) estimates, in contrast to exposed TcB estimates (0.52). However, even when comparing non-exposed TcB with TSB, there was a wide range of agreement limits (-3.8 to 4.6 mg/dL). Decisions based on non-exposed TcB values would have been incorrect in 26.6% of the cases. Conclusion Although there is a relatively strong correlation between total serum and TcB in non-PHT-exposed regions, the difference is not narrow enough to be utilized in guiding clinical decisions on the duration of PHT.