Posttransfusion purpura secondary to an alloantibody reactive with HPA-5a (Brb)

BACKGROUND: Posttransfusion purpura (PTP) is characterized by severe thrombocytopenia following blood transfusion that results from alloimmunization to platelet-specific alloantigens. Most cases involve antibodies against HPA-1a in homozygous HPA-1b persons. CASE REPORT: A patient developed PTP after cardiopulmonary bypass associated with a platelet-specific antibody with strong reactivity against HPA-5a (Br-b). Genotyping confirmed that the patient was homozygous for HPA-5b. CONCLUSION: This is the first well-documented occurrence of PTP associated with isolated allosensitization to HPA-5a or Br-b. The case highlights the importance of maintaining a high level of suspicion for PTP in the appropriate clinical setting, even in an atypical patient.