What is the most common cause of posttransfusion purpura?

Posttransfusion purpura (PTP) is a serious condition characterized by a sudden drop in platelet count and the appearance of purpura following a blood transfusion. The most common cause of PTP is the development of antibodies against human platelet antigens (HPAs), particularly anti-HPA-1a, which is associated with the immune response to transfused platelets.

When an individual receives a platelet transfusion, if they have been sensitized to certain HPAs through pregnancy or previous transfusions, they may produce antibodies that target these antigens on the transfused platelets. Anti-HPA-1a is the most frequently encountered antibody implicated in PTP. When these antibodies bind to the platelets, they mark them for destruction by the patient's immune system, leading to thrombocytopenia and the subsequent development of purpura.

This immune-mediated destruction is a hallmark of PTP, differentiating it from other potential causes of thrombocytopenia following a transfusion. In contrast, the other listed options do not play a significant role in the development of posttransfusion purpura. For example, antibodies against ABO blood group antigens (such as anti-A) do not typically lead to thrombocytopenia, and