Detection of individual false-low total bilirubin results in neonates and young infants using the bilirubin-to-icteric index ratio.

OBJECTIVE: Individual analytical errors in neonatal and infant bilirubin testing may pose serious clinical risk, for example, when very small samples are incompletely aspirated without triggering analyser error flags, causing falsely low results which may mask dangerous levels. Because the routinely measured icteric index (ICT) correlates with bilirubin, we evaluated whether a total bilirubin-to-icteric index ratio (TBIL/ICT) could identify discrepantly low TBIL results. METHODS: The study comprised two phases. In the threshold-derivation phase, routinely reported TBIL results were reviewed for infants aged ≤90 days with ICT >26 from Abbott Alinity platforms across three laboratories between June 2023 and May 2024. Visual outliers in the TBIL-ICT relationship were used to derive a TBIL/ICT threshold. The derived threshold was implemented, and triggered cases were reviewed over 19 months from June 2024 to December 2025 in the post-implementation assessment phase. RESULTS: In the derivation cohort of 12,057 qualifying samples, TBIL correlated strongly with ICT (Pearson r = 0.918, p < 0.001; Passing-Bablok regression TBIL = 0.708 × ICT + 13.361). Forty-nine samples (0.41%) were classified as visual outliers. A TBIL/ICT threshold <0.54 detected all visual outliers, with 99.9% specificity and 84.5% positive predictive value (PPV) against visual outlier classification. During the post-implementation assessment, 69 (0.19%) of 35,820 eligible samples triggered the TBIL/ICT <0.54 threshold. Of these, 55 (79.7%) were classified as individual false-low TBIL errors, seven (10.1%) as genuine results, and seven were unclassifiable. PPV was 79.7% for all flagged samples, and 88.7% when excluding unclassifiable samples. CONCLUSION: A TBIL/ICT ratio < 0.54 demonstrated a good PPV in detecting false-low TBIL results in infants on the Abbott Alinity system and provided a feasible, low-burden safeguard. Platform-specific validation is required before the adoption of TBIL/ICT on other systems.