Bilirubin-albumin molar ratio for screening high unbound bilirubin across gestational ages

The 2022 AAP Guideline recommends using the bilirubin-albumin molar ratio (BAMR) as an index of unbound bilirubin (UB) levels in term newborns. This study evaluated whether BAMR can reliably screen elevated UB levels across newborns of various gestational ages (GAs) during the first two weeks of life.

This retrospective observational study included newborns delivered between 2022 and 2023, categorized into four groups by GA: 22-27, 28-31, 32-36, and ≥37 weeks. Correlations between BAMRs and UB levels were analyzed. Estimated UB from BAMRs was compared with measured UB using Bland-Altman plots. Receiver operating characteristic (ROC) curves identified BAMR thresholds for UB ≥ 0.8 μg/dL.

BAMRs correlated significantly with UB across all groups (Rrm = 0.823-0.891). Bland-Altman analyses showed 95% limits of agreement of approximately -0.25 to 0.25 μg/dL. BAMR thresholds identifying UB ≥ 0.8 μg/dL were 0.35-0.47, with areas under ROC curves of 0.880-0.982.

In early postnatal period, BAMR shows strong correlations with UB levels across GA groups, including preterm newborns. Although it does not allow precise UB quantification, BAMR may serve as a screening tool to identify newborns with high UB who are at risk of bilirubin neurotoxicity.

Bilirubin-albumin molar ratio (BAMR) strongly correlates with unbound bilirubin (UB) levels across all gestational ages, including in preterm newborns. BAMR is inaccurate to quantify the UB level, but it may provide an estimate. While BAMR may serve as a screening tool, it should never be used as a stand-alone diagnostic method. These findings support broader clinical use of BAMR and may inform future guidelines for neonatal hyperbilirubinemia across all gestational ages.