Post-transfusion purpura is a rare complication characterised by paradoxical destruction of autologous platelets 5-10 days after transfusion of cellular blood products.

A middle-aged multiparous woman presented with mucocutaneous bleeding and severe thrombocytopenia seven days after aorta graft surgery and platelet transfusion. Initial treatment with steroids and intravenous immunoglobulin was ineffective. Platelet antibody testing showed anti-HPA-1a at a very high level of > 600 IU/mL, weak anti-HPA-3a and platelet auto-reactivity. Weakly reactive anti-HLA class I antibodies were also observed. The patient's platelet type was HPA-1bb/HPA-3bb. A diagnosis of post-transfusion purpura was therefore made. Additional treatment with plasma exchange was initiated, resulting in rapidly rising platelet counts, resolution of bleeding symptoms and decreasing antibody levels. Sustained normal platelet counts were achieved on day 50 after the initiating event.

This case represents a classic presentation of post-transfusion purpura, with high levels of anti-HPA-1a and severe thrombocytopenia with bleeding one week after transfusion, successfully treated with a combination of plasma exchange and intravenous immunoglobulin. Direct platelet antibody testing was positive during the thrombocytopenic phase and became negative following normalisation of the platelet count. This correlation between autoreactivity and thrombocytopenia supports the hypothesis of a secondary autoreactive process trigged by an HPA-incompatible transfusion.