Posttransfusion Purpura (PTP)
Posttransfusion purpura (PTP) is a rare but potentially life-threatening transfusion reaction characterized by severe thrombocytopenia occurring 5 to 10 days after a transfusion of blood products. This alloimmune disorder predominantly affects previously sensitized individuals and is most commonly associated with antibodies against human platelet antigen-1a (HPA-1a). The sudden and profound drop in platelet count places