Three patients highlighting potential pitfalls in platelet refractory testing

Abstract

AbstractBackgroundPlatelet‐transfusion refractory (PR) patients do not achieve expected post‐transfusion platelet counts. We investigate suspected PR patients with post‐transfusion platelet counts, indirect platelet antibody screens (ind‐PAS), Class I HLA antibody tests (HLA‐Scr), and physical platelet crossmatch (PXM) studies.Study Design and MethodsThe three following cases describe possible pitfalls of laboratory tests used in PR workup and management.ResultsCase #1: Antibody testing detected antibodies to only HLA‐B13, corresponding to a 4% calculated panel reactive antibodies (CPRA; 96% predicted donor compatibility). However, PXM showed the patient compatible with 11/14 (79%) donors; two of the PXM‐incompatible units were ABO‐incompatible. Case #2: PXM revealed compatibility with 1/14 screened donors; however, the patient did not respond to the product from the compatible donor. The patient did respond to HLA‐matched product. Dilution studies provided evidence of the prozone effect, which caused negative PXM despite clinically relevant antibodies. Case #3: There was a discrepancy between the ind‐PAS and HLA‐Scr. Ind‐PAS was negative for HLA antibodies, while HLA‐Scr was positive and specificity testing corresponded to 38% CPRA. Per the package insert, the sensitivity of ind‐PAS is ~85% compared to HLA‐Scr.DiscussionThese cases highlight the importance of investigating incongruent results. Cases #1 and #2 demonstrate PXM pitfalls: ABO incompatibility can result in positive PXM and false‐negative PXM can occur in the setting of the prozone effect. Case #3 reveals the importance of knowing a test's sensitivity. Centers that only perform ind‐PAS may fail to detect HLA antibodies.