Transfusion medicine

• Post-transfusion purpura is a rare but serious complication of a blood component transfusion in which severe thrombocytopenia occurs 5 - 10 days after the transfusion event
• Bleeding may be severe
• Risk of significant morbidity from bleeding complications with a > 10% mortality rate
• Self limiting but due to the severity of complications treatment is warranted
• IVIG is the mainstay of treatment

• Antiplatelet alloantibodies to human platelet antigens (HPA), usually due to prior transfusion, transplant or pregnancy
• Anti-HPA-1a is the most common culprit
• Other HPA antibodies have been implicated
• Anti-HPA antibody destroys autologous platelets; mechanism is not fully understood
  • Passive transfer of antibody is possible (Br J Haematol 1987;66:113)
  • Possible autoimmune platelet antibody masked by alloantibody (Transfus Med 2005;15:243)
  • Antibody to autologous GPIIb/IIIa platelet receptor (Am J Hematol 2016;91:848)
  • Immune complex binding to platelets (Vox Sang 1991;60:40)
  • Adhesion of transfused alloantigen to autologous platelets (Br J Haematol 1989;72:539)

• Symptoms:
  • Severe, sudden thrombocytopenia (< 10K/uL)
  • Bleeding (mucosal or gastrointestinal)
  • Petechiae or purpura

A 75 year old man with type II diabetes and hypertension is admitted for emergent cardiac catheterization due to an episode of chest pain with elevated cardiac enzymes. During the catheterization he requires 2 units of RBC and 1 unit of platelets for unexpected bleeding. He is stabilized and discharged after 48 hours. Six days later, he returns to his PCP with diffuse bruising and a platelet count of 9K/uL. Which item of clinical history is most pertinent to the diagnosis?

1. The patient was taking clopidogrel
2. The patient was in a motor vehicle accident 15 years ago, requiring multiple blood products
3. The patient has an allergy to trimethoprim-sulfamethoxazole
4. The patient has a sister with a history of heavy menses and easy bruising
5. The patient’s diabetes is poorly controlled with an A1C of 12.2%

B. The patient is exhibiting post-transfusion purpura. Although this is rare and less common in males, it can occur, particularly as a patient’s comorbidities increased. Prior exposure to foreign platelet antigens, through transfusion, transplant or pregnancy can result in antihuman platelet antigen antibodies. This patient’s prior history of blood transfusion and the sudden severe thrombocytopenia (< 20K/uL) occurring 5 - 10 days after a blood transfusion is consistent with PTP. Clopidogrel is an antiplatelet medication used in patients with increased risk of cardiac events or other hypercoagulable states, it does not cause thrombocytopenia but rather a iatrogenic thrombocytopathy. Trimethoprim-sulfamethoxazole is a common culprit in drug induced thrombocytopenia. There is no evidence that this patient would have received this medication. A sister with heavy menses and easy bruising suggests von Willebrand’s Disease (vWD). Although this is an autosomal dominant condition, even if the patient had vWD, it would not cause thrombocytopenia 5 - 10 days after a surgery. Poorly controlled diabetes can contribute to peripheral neuropathy, which can result in increased bruising or other injuries since patients do not feel the event. It does not affect the platelet count.

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Reference: Post-transfusion purpura (PTP)

A 62 year old woman is admitted for urosepsis and anemia. The clinical team calls you because they are preparing to give an RBC transfusion but the patient’s daughter is refusing the transfusion. The daughter says during a previous transfusion at a different hospital her mom had low platelets and severe bruising. You tell the clinical team that you recommend which of the following?

1. The patient should receive leukocyte-reduced red cells and the team should provide reassurance to the daughter
2. The patient should receive crossmatched platelets due to presumed HLA antibodies
3. The patient should receive IgA deficient plasma
4. The patient should receive washed RBCs to prevent post-transfusion purpura
5. The patient may have an antibody and should receive phenotypically matched RBCs

D. The history the daughter has provided suggests a prior history of post-transfusion purpura in the patient. Post-transfusion purpura carries a high risk of morbidity and mortality. Even though recurrence is exceedingly rare, washed products (to remove the offending HPA antibody) or matched products (it the HPA type is known) is recommended. Although HLA antibodies could be a concern in a multiparous woman, one would typically give an unmodified (other than leukocyte reduction) platelet and monitor the post-transfusion platelet count before assuming that crossmatching is needed. IgA deficient plasma is a rare, special order product that is given for patients with proven severe allergic reaction to IgA. If the patient has an antibody to a red cell antigen, that should be identified during routine type and screen, although it would be prudent to contact the prior hospital for history of any antibody that have become undetectable.

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Reference: Post-transfusion purpura (PTP)