Updated project metadata. During the COVID-19 pandemic, Multisystem Inflammatory Syndrome in Children (MIS-C) emerged as a disease with unknown causes and no specific diagnostic test. We used artificial intelligence in a nationwide study from April 2020 to March 2022 to identify a 4-protein diagnostic signature for MIS-C. This signature had an AUC of 1.0 for distinguishing MIS-C from other febrile diseases. Our analysis also revealed intricate protein patterns, indicating that MIS-C is associated with immune dysregulation, lipid metabolism changes, increased coagulation activity, and tissue remodeling.