Gestational Age-Specific Agreement Between TcB Measured at the Sternum or Upper Back and Serum Bilirubin

Transcutaneous bilirubin (TcB) measurement is widely used for noninvasive jaundice screening, but evidence regarding its correlation and agreement with serum bilirubin across gestational ages (GAs) remains limited, particularly in preterm newborns. At our institution, TcB screening is routinely performed at the sternum or upper back. This study evaluated the relationship between TcB measured at these sites and total serum bilirubin (TsB) across GAs.

This retrospective study included newborns born at 28-41 weeks' gestation and admitted to a tertiary pediatric referral center between January 2020 and December 2023. Paired TcB and TsB measurements obtained within a 1-h interval during Postnatal Days 0-13 were analyzed. Newborns were grouped by GA (28-31, 32-36, and 37-41 weeks). Correlation was assessed using repeated-measures correlation, and agreement using Lin's concordance correlation coefficient (LCCC) and Bland-Altman analysis.

A total of 1668 paired TcB-TsB measurements from 893 newborns were analyzed. TcB and TsB showed strong correlations in all groups (Rrm = 0.873, 0.897, and 0.880; all p < 0.001), whereas LCCC values were 0.618, 0.707, and 0.766, respectively. TcB tended to overestimate TsB, with mean biases of 2.2, 2.3, and 1.7 mg/dL and lower limits of agreement of -1.4, -1.5, and -2.8 mg/dL, respectively.

TcB measured at the sternum or upper back showed strong correlations with TsB across GAs from 28 to 41 weeks, although absolute agreement was more limited. TcB may serve as a screening tool when its bias and limits of agreement are considered.