A 28-year-old woman presents with a 2-day history of severe epistaxis and gum bleeding. She has a history of easy bruising since childhood. On examination, she has petechiae on the lower extremities and a palpable spleen. Hemoglobin is 9.2 g/dL, WBC 7,500/μL, and platelet count 8,000/μL. Peripheral blood smear shows no schistocytes. Coagulation studies and fibrinogen are normal. What is the most appropriate next step in management?