Post-Transfusion Purpura

Happy Friday, Moffitt!

Thank you to Ashley, for presenting the case of a middle-aged woman who developed severe, post-operative thrombocytopenia. We discussed our approach to thrombocytopenia, with a specific focus on immune mediated processes (HIT, drug-induced, ITP etc). In the end, the patient as diagnosed with an extremely rare diagnosis of post-transfusion purpura. Wow! More pearls below. 🙂



TOP PEARLS (from Pat Cornett)

  • The morphology of platelets on a blood smear can tell you a lot about the mechanism of thrombocytopenia! For small platelets, think decreased production and increased sequestration. For large platelets, think increased destruction or consumptive processes.
  • Approach thrombocytopenia by categorizing them into 4 big processes: 1) BM suppression; 2) platelet destruction/consumption; 3) dilution; and 4) redistribution/splenomegaly
  • Post-transfusion purpura (PTP) is an extremely rare transfusion reaction secondary to production of anti-platelet antibodies in the recipient of blood transfusion.


Post-Transfusion Purpura (PTP) – What is it?

  • An extremely rare transfusion reaction (only ~250 cases reported!)
  • It is a delayed transfusion reaction involving platelets, where the recipient of a blood transfusion forms antibodies against human platelet antigen 1a (HPA-1a). These antibodies cause destruction of the transfused platelets as well as the recipient’s native platelets, leading to thrombocytopenia.
  • 97-99% of whites and 99% of blacks are HPA-1 antigen positive. In those without this antigen, sensitization can occur during transfusions or pregnancy (ie upon exposure to the antigen on fetal platelets)!
  • Usually, PTP is associated with severe thrombocytopenia (Plt count < 30K) and leads to purpura, petechiae, and clinically significant bleeding!
  • Onset is usually 5-10 following transfusion, and thrombocytopenia lasts days to weeks!
  • Diagnosis is confirmed by checking the antibody level to HPA-1a + demonstrating lack of this antigen on the patient’s own platelets (this is a send-out test to the Blood Center of Wisconsin)
  • Always consider other immunologically mediated forms of thrombocytopenia in the differential – ITP, TTP, drug-induced thrombocytopenia (including HIT)!
  • Treatment is IVIG (for about 5 days) and glucocorticoids. Transfusion of platelets is generally not effective, because most platelets (even antigen-negative platelets) are destroyed by antibodies.

Blast from the Past: ITP Pearls!

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