Post-transfusion purpura (PTP)

When to suspect this adverse reaction?

PTP is a rare delayed transfusion reaction where a patient develops dramatic, sudden and self-limiting thrombocytopenia (platelet counts <10 x 109/L in 80% of cases), typically 7 to 10 days after a blood transfusion.

Bleeding from mucous membranes and the gastrointestinal and urinary tracts is common. Mortality is rare but may be due to intracranial haemorrhage.(1,2) Thrombocytopenia is expected to last approximately 2 weeks.(2)

Patients usually have a history of sensitisation by either pregnancy or transfusion with five times more female patients affected than males.(1,2)
 

Usual causes?

It is due to antibodies to platelet-specific antigens, most often Human Platelet Antigen 1a (HPA-1a), however antibodies to HPA-1b, other platelet antigens and HLA antigens have also been implicated in PTP.

The immune specificity is against a platelet-specific antigen yet both autologous and allogeneic platelets are destroyed. The mechanism of autologous platelet destruction is unclear.(1,2)
 

Investigation

Demonstrate antiplatelet antibody in the patient’s plasma. 
 

What to do?

Give intravenous immunoglobulin at 1 g/kg as a single dose and repeat as necessary,(3) the platelet count is expected to rise in the next 4 days. Steroids and plasma exchange may be tried in refractory cases.(1,4)

Antigen-negative red cells and platelets may be indicated if subsequent transfusion is required but this is controversial.(2)
 

References
  1. Fung MK (ed).  Non-infectious complications of blood transfusion.  Chapter 27, AABB Technical Manual, 18th edition.  AABB, Bethesda, 2014.
  2. Callum JL, Pinkerton PH, Lima A, Lin Y, Karkouti K, Lieberman, L, et al. Chapter 5, Transfusion Reactions. Bloody Easy 4: Blood Transfusions, Blood Alternatives and Transfusion Reactions: A Guide to Transfusion Medicine, 4rd edition. Canada: Ontario Regional Blood Coordinating Network, 2016.  Available from: http://transfusionontario.org/en/download/bloody-easy-4-blood-transfusio...

  3. Criteria for the Clinical Use of Intravenous Immunoglobulin in Australia, July 2016.  National Blood Authority.  Australia. Avalilable from: https://www.criteria.blood.gov.au/

  4. Delaney M, Wendel S, Bercovitz R, Cid J, Cohn C, Dunbar D,et al.  Transfusion reactions:prevention, diagnosis and treatment.  BJH 2016; 388: 2825-36.