Implementation of a reformulated Roche® bilirubin Gen.3 reagent did not affect the relationship between BiliChek transcutaneous and Roche total serum bilirubin

Refining interpretation of transcutaneous bilirubin measurement in newborns born late preterm

BACKGROUND

Transcutaneous bilirubin (TCB) monitoring is widely used for jaundice screening in the newborn period. Limited data exists on adjusting TCB for bias in late preterm infants. The objective of this study was to determine the median bias between transcutaneous bilirubin and total serum bilirubin levels in newborns born at 35-36 weeks' gestation.

METHODS

This was a retrospective cohort study of late preterm infants born at 35-0/7 to 36-6/7 weeks' gestation who were admitted to a level III neonatal intensive care unit from May 2018 to February 2020. Transcutaneous and total serum bilirubin levels were assessed within 2 h of each other during the first 60 h of life. Bland-Altman plots were used to evaluate transcutaneous bilirubin bias. Bilirubin risk stratification based on age (in hours) was done using an adaptation of the Bhutani nomogram for transcutaneous, adjusted transcutaneous, and total serum bilirubin measurements.

RESULTS

The median bias between transcutaneous and total serum bilirubin bias was 2.4 mg/dL (IQR 1.7-3.4, 95% CI 2.2-2.7). The kappa statistic demonstrated slight agreement between the unadjusted transcutaneous bilirubin and total serum bilirubin (k = 0.033, p = 0.194. The kappa statistic demonstrated fair agreement between an adjusted transcutaneous bilirubin (subtract 1 mg/dL) and total serum bilirubin (k = 0.298, p < 0.0001) and moderate agreement between another adjusted transcutaneous bilirubin (subtract 2 mg/dL) and total serum bilirubin (k = 0.430, p < 0.0001).

CONCLUSION

In a single center study of late preterm infants, transcutaneous bilirubin systematically overestimated the total serum bilirubin level. Subtracting 1 mg/dL from the transcutaneous bilirubin identified infants with total serum bilirubin levels in the high or high intermediate risk range. Adjusting the transcutaneous bilirubin prior to risk stratification may reduce unnecessary blood draws for total serum bilirubin. Studies of racially and ethnically diverse newborns using various transcutaneous bilirubin meters are needed prior to broad application of the adjusted transcutaneous bilirubin approach.

Error simulation modeling to assess the effects of bias and precision on bilirubin measurements used to screen for neonatal hyperbilirubinemia

OBJECTIVES

Error simulation models have been used to understand the relationship between analytical performance and clinical outcomes. We developed an error simulation model to understand the effects of method bias and precision on misclassification rate for neonatal hyperbilirubinemia using an age-adjusted risk assessment tool.

METHODS

For each of 176 measured total bilirubin (TSB_M) values, 10,000 simulated total bilirubin (TB_S) values were generated at each combination of bias and precision conditions for coefficient of variation (CV) between 1 and 15%, and for biases between -51.3 μmol/L and 51.3 μmol/L (-3 and 3 mg/dL) fixed bias. TB_S values were analyzed to determine if they were in the same risk zone as the TSB_M value. We then calculated sensitivity and specificity for prediction of ≥75th percentile for postnatal age values as a function of assay bias and precision, and determined the rate of critical errors (≥95th percentile for age TSB_M with <75th percentile TB_S).

RESULTS

A sensitivity >95% for predicting ≥75th percentile bilirubin values was observed when there is a positive fixed bias of greater than 17.1 μmol/L (1.0 mg/dL) and CV is maintained ≤10%. A specificity >70% for predicting <75th percentile bilirubin values was observed when positive systematic bias was 17.1 μmol/L (1 mg/dL) or less at CV ≤ 10%. Critical errors did not occur with a frequency >0.2% until negative bias was -17.1 μmol/L (-1 mg/dL) or lower.

CONCLUSIONS

A positive systematic bias of 17.1 μmol/L (1 mg/dL) may be optimal for balancing sensitivity and specificity for predicting ≥75th percentile TSB values. Negative systematic bias should be avoided to allow detection of high risk infants and avoid critical classification errors.