Post Transfusion Purpura
Post-transfusion purpura (PTP) is characterized by an abrupt drop in platelet count in the first 3 weeks after platelet transfusion. Affected individuals have a prior history of sensitization to platelet antigens from pregnancy or previous transfusion. Upon subsequent transfusion the recipient mounts an anamnestic antibody response against a platelet specific antigen on the donor platelets, that he or she lacks. In most cases the antibody is directed towards HPA-1 antigen. Thrombocytopenia occurs between 1 and 24 days (mean 9 days) after transfusion.
Through some unknown mechanism, recipient’s own antigen negative platelets are destroyed along with transfused antigen positive platelets. Thrombocytopenia is often severe with platelet counts falling below 10, 000/uL. The National Healthcare Safety Network (NHSN) hemovigilance criterion is that the post-transfusion platelet count decreases to less than 20% of the pre-transfusion platelet count.
Thrombocytopenia may persist for several weeks if not treated. Mortality rates between 10 and 15% have been reported. Treatment usually consists of intravenous immune globulin (IVIG), corticosteroids, or both.
Even though a patient’s own antigen negative platelets have been destroyed, transfusion of HPA-1 antigen negative platelets may be efficacious in life threatening situations, such as intracranial hemorrhage.
