Correlation Between Transcutaneous Bilirubin and Serum Bilirubin in Preterm Neonates in Neonatal Jaundice: A Prospective Observational Study

Objective

To determine the correlation between transcutaneous bilirubin (TcB) and total serum bilirubin (TSB) in preterm neonates, and assess this correlation in two gestational sub‐groups before and after phototherapy.

Methods

This prospective observational study was conducted in a tertiary Neonatal Intensive Care Unit on preterm neonates (28 to 34 ⁺⁶ weeks) screened for neonatal jaundice, with TcB measurements and TSB levels obtained within 2 h. In neonates requiring phototherapy, photoprotective patches were applied to the forehead and sternum for TcB measurements, repeated 24 h after phototherapy. Paired data analysis was performed using correlation coefficients and Bland–Altman plots.

Results

A total of 399 paired samples from 154 neonates were analysed. In overall pooled measurements, TcB showed a consistent positive bias relative to TSB, with mean differences of 1.19 ± 1.42 mg/dL at the forehead and 1.25 ± 1.62 mg/dL at the sternum, with wider limits of agreement at the sternum. Correlation with TSB remained high at both sites, with slightly higher correlation at the forehead ( r  = 0.921) than at the sternum ( r  = 0.913). The 32–34 ⁺⁶ weeks gestational subgroup showed slightly higher correlations ( r  = 0.930) and smaller mean differences (1.19 ± 1.32 mg/dL) than the 28–31 ⁺⁶ weeks subgroup ( r  = 0.910, mean difference = 1.19 ± 1.53 mg/dL), particularly at the forehead. After phototherapy, forehead measurements showed reduced mean bias compared with prior to phototherapy measurements, although limits of agreement remained wide, while sternal measurements demonstrated greater variability and a tendency to underestimate TSB.

Conclusion

TcB demonstrated moderate agreement with TSB, with a tendency to overestimate bilirubin levels, while maintaining a strong correlation in early and moderate preterm neonates. Agreement was relatively better at the forehead and in higher gestational age groups. It serves as a useful non‐invasive screening and adjunctive tool to reduce blood sampling. However, TSB remains essential for definitive clinical decision‐making.

Trial Registration: CTRI/2023/02/049478