Post-transfusion purpura

Post-transfusion purpura (PTP) is an adverse reaction to a blood transfusion 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, a rapid decline in platelet count.^[1] PTP usually presents 5–12 days after transfusion, and is a potentially fatal condition.

PTP is rare, but usually occurs in women who have had multiple pregnancies or in people 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). The patient develops antibodies to the HPA-1a antigen leading to platelet destruction. In some cases, HPA-5b has also been implicated. It is unclear why alloantibodies attack the patient’s own, as well as the introduced platelets. Probable explanation for this is that the recipient’s platelet acquire the phenotype of donor’s platelet by binding of the soluble antigens from the donor onto the recipient’s platelet.^[2]

It is usually self-limiting, but IVIG therapy is the primary treatment.^[3] Plasmapheresis is also an option for treatment.^[4]

• Blood transfusion
• Neonatal alloimmune thrombocytopenia