Posttransfusion Purpura

GENERAL PRINCIPLES

Definition

Posttransfusion purpura (PTP), a rare syndrome characterized by the formation of alloantibodies against platelet antigens, most commonly HPA-1a, follows blood component transfusion and causes severe thrombocytopenia.

Epidemiology

PTP has an incidence of 1 in 50,000-100,000 blood transfusions, although approximately 2% of the population has a potential risk for PTP based on the frequency of HPA-1b#8725;1b.

Etiology

Glycoprotein (GP) IIIa has a polymorphic epitope called HPA-1a#8725;b, the antigen most commonly involved in PTP. PTP typically occurs in HPA-1a#8725;1b-negative multiparous women or previously transfused patients when re-exposed to HPA-1a by transfusion. An amnestic response produces alloantibodies to the HPA-1a, which appear to also recognize the patient's HPA-1a-negative platelets and cause thrombocytopenia via platelet destruction.

DIAGNOSIS

• InPTP, severe thrombocytopenia (lt;15 ? 10⁹#8725;L) usually occurs within 7-10 days of transfusion.

• Confirmation of suspected PTP requires detection of platelet alloantibodies.

TREATMENT

Although spontaneous platelet recovery eventually occurs, bleeding may require treatment. Effective therapies include IVIG and plasmapheresis. Transfusion with platelets from a donor who lacks the causative epitope (typically HPA-1a) does not clearly have higher efficacy than random platelet transfusion. Reserve transfusion for patients with PTP and severe bleeding.²⁷