Emory University School of Medicine, Georgia, United States
Background/Case Studies: Patients with immune-mediated platelet transfusion refractoriness (PTR) caused by anti-platelet glycoprotein (GP) and/or anti-HLA antibodies (HLA-Ab) may benefit from transfusion with crossmatch (XM)- or HLA/HPA-compatible platelets. At our institution, immune-mediated PTR is investigated by indirect platelet antibody (PLT-Ab) screen, HLA-Ab testing, and physical platelet XM. In this case report, we describe a complicated investigation of PTR in a 47-year-old female with relapsed acute myeloid leukemia that developed warm autoantibody (WAA).
Study
Design/Methods: Plt-Ab screen by ELISA-based Pak-Plus (Immucor) and flow cytometry-based Pak-Lx (Immucor). Flow cytometry-based HLA-Ab screen and identification by FlowPRA/LABScreen (OneLambda) and LIFECODES Class I/LSA (Immucor). Physical platelet XM by Solid Phase Red Cell Adherence Assay (Immucor).
Results/Findings: In this patient, Plt-Ab screen by ELISA was positive for anti-GPIa/IIa, GPIIb/IIIa, GPIb/IX, GPIV, and HLA class I. HLA-Ab screen showed PRA of 45% and identified numerous HLA class I antibodies (Table 1). Physical platelet XM was compatible with 14/14 donors. Based on the Plt-Ab and HLA-Ab results only about half should have been compatible by chance. The initial Plt-Ab screen was false positive since repeat ELISA showed panagglutinin pattern and flow cytometry was negative for anti-platelet GP and HLA-Ab. Repeat HLA-Ab tests consistently detected A2, A3, A23, B7, B8, B55, B57, and B58 (Table 1). Physical platelet XM showed prozone effect with neat plasma compatible with 4/4 donors but incompatible with 2/4 donors after dilution (1:4-1:8). This pattern can be explained by A2 and B8 HLA-Ab against donor #1 (A2) and #2 (B8); B7 HLA-Ab was detectable but at insufficient level to cause incompatibility in donor #3 (B7). Conclusions: This case report demonstrates the pitfalls of relying on any single method to evaluate immune-mediated PTR. Plt-Ab screens are prone to WAA interference and lack sensitivity to HLA-Ab due to limited HLA antigen panel. HLA-Ab testing may detect antibodies at levels that do not cause XM-incompatibility. The solid phase platelet XM assay can run afoul of the prozone effect. Combined assessment is crucial for selecting compatible platelets in PTR patients.
Importance of research: Transfusion programs must carefully consider the potential pitfalls of commonly employed methods used to evaluate immune-mediated platelet transfusion refractoriness and select compatible platelets. Panagglutinin interference on platelet antibody screen, relative sensitivity for HLA antibody detection depending on assay type, prozone effect in solid phase crossmatch, and discrepancy between detected and incompatible HLA antibodies are demonstrated in this case report.
