Discrepancy between Transcutaneous and Serum Bilirubin Measurement in Healthy Chinese Newborns in a Baby-friendly Hospital in Hong Kong

Abstract

Objective: To characterise the discrepancy between transcutaneous bilirubin (TcB) and total serum bilirubin (TSB) levels and to evaluate the use of TcB measurements in  detection of severe hyperbilirubinaemia requiring phototherapy among healthy Chinese newborns.
Methods: Medical records were reviewed to collect data on paired TcB-TSB  measurements. The paired TSB level was obtained within 2 hours of the TcB measurement in healthy Chinese neonates admitted to one of our postnatal wards over a 1-year period, from January to December 2015. Demographic information and outcome for individual newborns were also recorded. TcB-TSB differences were calculated and analysed in order to obtain their correlations. Multivariate regression analysis was used to identify characteristics independently associated with TcB-TSB difference of ≥20 and ≥30 μmol/L. The clinical application of TcB, together with Bhutani nomogram in the prediction of severe hyperbilirubinaemia in medium- and higher-risk thresholds for phototherapy was also analysed.
Results: A total of 220 TSB levels were matched with a TcB value. The correlation between paired measurements was 0.75. The mean TcB-TSB difference was 28.76±23.83 μmol/L. TcB measurements in general tended to overestimate TSB, although the TcB-TSB difference varied with different TSB values and TcB measurements tended to be underestimated as TSB levels increased. Using the 75th centile tract of Bhutani nomogram as threshold, TcB measurements could predict all cases in the high-risk zone with a sensitivity and negative predictive value of 100% each. At medium-risk and higher-risk thresholds for phototherapy, using the 75th centile as the cut-off level, the sensitivity was 93.2% and 73.1%, respectively.
Conclusions: TcB measurement provided a reasonable estimate of TSB in healthy newborns with a high breastfeeding rate. As TcB-TSB difference varied with different TSB levels, caution should be taken especially in cases with severe hyperbilirubinaemia in which TcB measurements tended to be underestimated with higher TSB level. Combining the use of TcB measurements and the 75th centile tract of Bhutani nomogram as the cut-off level can detect all high-risk cases of severe hyperbilirubinaemia.