Comparison of transcutaneous bilirubin with serum bilirubin in newborn unit: A cross sectional study

Background: Transcutaneous Bilirubin (TcB) is a non invasive, point of care test for assessing bilirubin level. There has been renewed interest in use of this method with availability of newer generation transcutaneous bilirubinometer (Bilichek and JM-103). Indian studies evaluating TcB with newer generation bilirubinometer have limitations of small sample size, inclusion of mainly term neonates and focusing only on correlation between the two methods (ignoring agreement between the two)
Methods:This cross-sectional study enrolled 200 healthy neonates (<34 weeks-25, 34-37 weeks-76, >37 weeks-99) who were judged to have clinically significant jaundice and required TSB estimation. TcB was measured at forehead using TcB meter (DRAGER, JM-103) within 30 minutes of obtaining sample for TSB. TcB -TSB difference was computed.
Results: Mean (±SD) TcB-TSB difference was 0.68±2.12 mg/dL (range -5.6 to 6.9 mg/dL). Corresponding difference in preterm and term babies was 1.20±1.92 mg/dL (range -4.1 to 5) and 0.15±2.19 mg/dL (range -5.6 to 6.9 mg/ dL) respectively. Correlation between TcB and TSB was good across various gestational ages (r value 0.75 overall and 0.71, 0.74 and 0.74 in 30-34 weeks, 34-37 weeks and >37 weeks gestational age, respectively) and between TSB values of 10-18 mg/dL (r-value 0.79). However, correlation was poor when TSB was less than 10 mg/dL and moderate at TSB level above 18 mg/dL (r value 0.36 and 0.65, respectively). Clinically relevant discrepancy of ≥±3 mg/dL between TcB and TSB was present in 17% of study subjects.
Conclusions: TcB correlates well with TSB in TSB range of 10-18 mg/dL but agreement between two methods is not good and underestimation by TcB at higher values of TSB is a concern. So, TcB is not a substitute for TSB and should never be used in isolation.