1. A method of treating a human subject that has newly diagnosed, persistent, or chronic immune thrombocytopenia (ITP), the method comprising administering to the subject a human neonatal Fc receptor (hFcRn) antagonist, wherein the hFcRn antagonist is administered intravenously once weekly at a dose of about 5 mg/kg to about 10 mg/kg at least four times, wherein the hFcRn antagonist consists of a variant Fc region consisting of two Fc domains which form a homodimer, wherein the amino acid sequence of each of the Fc domains consists of SEQ ID NO: 1, SEQ ID NO: 2, or SEQ ID NO: 3, wherein the human subject has a platelet count of ≤30×10⁹/L on standard-of-care treatment with at least one compound approved for standard-of-care treatment for ITP prior to administering the hFcRn antagonist, and wherein the subject achieves a platelet count of >50×10⁹/L after administering four doses of the hFcRn antagonist, thereby treating the subject.