Relation of total serum bilirubin and transcutaneous bilirubin at different sites in term neonates: impact of phototherapy

Abstract Objective To find out correlation and agreement between total serum bilirubin (TSB) and transcutaneous bilirubin (TcB) at different sites in term neonates before, during, and after phototherapy. Methods This prospective repeated measures observational study was conducted at a tertiary care teaching hospital of western Rajasthan from June 2022 to December 2022. Term neonates (gestational age ≥ 37 weeks) requiring phototherapy were included. In each neonate TSB was estimated three times using the Diazo method; at baseline, 24 h after initiation of phototherapy, and 24 h after completion of phototherapy. Corresponding TcB readings were taken at one exposed area sternum, and two covered areas; glabella (eye-shield covered), and pubic symphysis (diaper-covered) using transcutaneous bilirubinometer. Pearson correlation and Bland Altman analyses were done to assess correlation and agreement between the two variables respectively. Results Out of 850 neonates screened, 130 were analyzed. Before phototherapy, TSB correlated strongly with TcB at the sternum (r = 0.83), with overestimation bias of 1.40 mg/dL on agreement analysis. During phototherapy, correlation coefficient of TSB and TcBwas equal for two sites; sternum and pubic symphysis (0.90 each), but on agreement analysis Lin’s concordance correlation coefficient was highest for the pubic symphysis(0.78) with underestimation bias of 0.88 mg/dl. After phototherapy again correlation coefficient of TSB and TcBwas equal for two sites; sternum and pubic symphysis, but on agreement analysis Lin’s concordance correlation coefficient was highest for the pubic symphysis with underestimation bias of 0.16 mg/dL. Conclusions TSB correlated maximally with TcB at sternum (before phototherapy), at sternum &pubic symphysis(during phototherapy and after phototherapy). But on agreement analysis least bias was noted between TSB and TcB at sternum (before phototherapy), and at pubic symphysis (both during and after phototherapy).