Post-transfusion purpura (PTP) is an adverse reaction to a blood transfusion

Blood transfusion

Blood transfusion is the process of receiving blood products into one's circulation intravenously. Transfusions are used in a variety of medical conditions to replace lost components of the blood...

 or platelet transfusion that occurs when the body produces alloantibodies to the introduced platelets' antigens. These alloantibodies destroy the patient's platelets leading to thrombocytopenia

Thrombocytopenia

Thrombocytopenia is a relative decrease of platelets in blood.A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease...

, a rapid decline in platelet count. PTP usually presents 5–12 days after transfusion, and is a potentially fatal condition.

Mechanism and treatment

PTP is rare, but usually occurs in women who have had multiple pregnancies or in men who have undergone previous transfusions. The precise mechanism leading to PTP is unknown, but it most commonly occurs in individuals whose platelets lack the HPA-1a antigen (old name: PL^A1) are transfused platelets that do contain the HPA-1a antigen. The patient develops antibodies to the HPA-1a antigen leading to platelet destruction. It is unclear why alloantibodies attack the patient's own, as well as the introduced platelets. It is usually self-limiting, but IV IgG therapy is the primary treatment. Plasmapheresis

Plasmapheresis

Plasmapheresis is the removal, treatment, and return of blood plasma from blood circulation. It is thus an extracorporeal therapy...

is also an option for treatment.