Allergic transfusion reactions (ATRs) occur within 24 h of transfusion. A less common but more severe manifestation of ATR is anaphylaxis. The relationship between the mechanisms underlying ATRs and donor, product, and/or recipient factors is not well understood. Our aim is to investigate the underlying factors responsible for eliciting anaphylactic ATRs and possibly identify the molecule responsible, that could routinely be used as a biomarker in subsequent pre-transfusion screens. We employ an IP-MS workflow for this purpose. Purified IgG antibodies from donor plasma are immobilized on magnetic beads and interacted with basophil cells lysates. The immunoprecipitants are analyzed by mass spectrometry.