A Study of Efgartigimod IV in Participants From 12 Years to Less Than 18 Years of Age With Chronic Immune Thrombocytopenia (ITP)

Inclusion Criteria: * Is aged 12 to less than 18 years when completing the informed consent process * Has a documented duration of primary ITP of more than 12 months on the date the informed consent process is complete * Has documented prior ITP treatment with at least 1 of the following treatments: corticosteroids, IVIg, anti-D immunoglobulin, thrombopoietin receptor agonist (TPO-RAs), or rituximab. * Has documented prior response, defined as 1 platelet count of ≥50 × 10\^9/L to at least 1 of the following ITP treatments: prednisone, other or nonspecified corticosteroids, IVIg, or anti-D immunoglobulin * Has documented insufficient response to a prior ITP treatment with corticosteroids, IVIg, anti-D immunoglobulin, TPO-RAs, rituximab, or splenectomy * Has documented mean platelet count of less than 30 x10\^9/L Exclusion Criteria: * Secondary ITP according to the following definition by the International Working Group (IWG): all forms of immune-mediated thrombocytopenia except primary ITP * Nonimmune thrombocytopenia * ITP-associated critical or severe bleeding * History of hereditary thrombocytopenia