Limitations
This study has limitations. While blood sample collection was performed according to the HEAL Trial manual of operations and we adjusted for site variability in our analyses, we cannot exclude the possibility that variability within sites with regards to handling and processing of samples may have affected results. The strength of associations between biomarkers and outcomes may also differ if other clinical covariates and neurodiagnostic assessment tools were considered in our analyses. Furthermore, only 180 of 500 potential samples were evaluated as guided by our power calculations and cost, and this may have increased the risk of bias. Future prospective validation of our models is warranted prior to incorporation of biomarker measurements into clinical care for neonates with HIE.