Post-transfusion purpura secondary to passive transfer of anti-P1A1 by blood transfusion.

A patient developed severe post-transfusion purpura (PTP) following transfusion of two units of packed red blood cells. The timing of the patient's thrombocytopenia suggested passive immunization rather than the typical anamnestic response associated with classical PTP. Investigation of the blood donors revealed one with evidence of a platelet specific antibody of high titre. This donor was typed as P1A1 negative and the antibody was shown to have anti-P1A1 specificity.