Of the other four biomarkers included in the model, MDC (1.6) and PDGF-AB/BB (1.4) are elevated in COVID-19 relative to MIS-C, while G-CSF (2.36) and FLT-3L (1.1) are elevated in MIS-C, consistent with the model’s robust performance across a range of de novo validation sets gathered even as the disease itself evolved. Here, CSF3 is linked to COVID-19.