Comparison of transcutaneous bilirubin under patch-covered skin with total serum bilirubin in neonates undergoing phototherapy

Transcutaneous bilirubinometry (TcB) is a recognized tool to monitor neonatal hyperbilirubinemia, demonstrating a high correlation with total serum bilirubin (TSB) before phototherapy. However, once phototherapy is started, TcB may become unreliable. To evaluate the correlation and agreement of TcB measured under variously patched skin at different sites (a coin over the sternum, eye shield over the forehead, and diaper area at the back) with TSB. One hundred and ten neonates requiring phototherapy were enrolled. TcB was noted at the three sites using a Drager JM-105 bilirubinometer. TSB was measured before and after phototherapy. Paired t-test, correlation, and Bland-Altman limits of agreement (LOA) analysis were performed. Before phototherapy, the mean TcB values (mg/dl) at the forehead, sternum, and back were 14.4 ± 3.25, 14.8 ± 3.06, and 12.05 ± 3.05, respectively, compared to TSB of 14.71 ± 3.35. All three sites showed a strong positive correlation between TcB and TSB, and the range of LOA (mg/dl) was the narrowest over the sternum (-2.99, 3.18). After phototherapy, the mean TcB values at the forehead, sternum, and back were 8.97 ± 2.98, 10.27 ± 2.87, and 7.92 ± 2.29, respectively, compared to the TSB of 10.78 ± 2.70. A decrease in correlation between TcB and TSB was noted over all the sites, with the best correlation remaining over the sternum (0.83). To conclude, the sternum showed the best LOA (-3.74, 2.73) among the three patch-covered sites. TcB at sternum with coin-patch displayed the best correlation and agreement with TSB, before and after phototherapy compared to the forehead and back.