Transcutaneous bilirubinometry during and after phototherapy in preterm infants: a prospective observational study

OBJECTIVE: To examine the accuracy of transcutaneous bilirubinometry (TCB) measurements during and after phototherapy (PT) in preterm infants. DESIGN: Prospective observational cohort study. SETTING: Level III neonatal centre. PATIENTS: Preterm infants (from 23+0 to 36+6 weeks of gestation) born between June 2017 and May 2018 requiring PT. INTERVENTIONS: TCB was measured from an exposed area of the skin (the sternum; TCBU) and the covered area of the skin under the nappy (the bony part of the upper outer quadrant of the buttock; TCBC) within an hour of obtaining total serum bilirubin (TSB). MAIN OUTCOME MEASURES: Correlation and agreement between TCB (TCBU and TCBC) and TSB during and after PT. RESULTS: We have enrolled 196 preterm infants. There was a significant correlation between TSB and TCB during PT (r=0.72, 95% CI 0.66 to 0.77 in covered area; r=0.75, 95% CI 0.70 to 0.80 in uncovered area) and after PT (r=0.87, 95% CI 0.83 to 0.91). TCB underestimated TSB level during PT, with a mean TCBC–TSB difference of −25±43 (95% agreement limits of 62 to −112) and a mean TCBU–TSB difference of −48±46 (95% agreement limits of 45 to −140). The agreement between TCB and TSB after cessation of PT improved, with TCB underestimating TSB by a mean TCB–TSB difference of −10±31 (95% agreement limits of 52 to −72). CONCLUSION: TCB measurements correlated strongly with TSB levels during and after PT. However, there was a wide and clinically relevant disagreement between TCB and TSB measurements during the PT phase, improving significantly after PT.