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Dimeric FcγR ectodomains detect pathogenic anti‐platelet factor 4–heparin antibodies in heparin‐induced thromobocytopenia
Author(s) -
Wines B. D.,
Tan C. W.,
Duncan E.,
McRae S.,
Baker R. I.,
Andrews R. K.,
Esparon S.,
Gardiner E. E.,
Hogarth P. M.
Publication year - 2018
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/jth.14306
Subject(s) - heparin , heparin induced thrombocytopenia , platelet factor 4 , antibody , medicine , platelet activation , platelet , immunology , pharmacology
Essentials FcγRIIa mediates life‐threatening heparin‐induced thrombocytopenia (HIT). Most anti‐platelet factor (PF)4‐heparin IgGs are not pathogenic so diagnosis of HIT is challenging. Dimeric rsFcγRIIa was used to quantify receptor‐binding activity of anti‐PF4‐heparin antibodies. Dimeric rsFcγRIIa binding specifically correlated with occurrence of HIT.Summary Background Heparin‐induced thrombocytopenia ( HIT ) is a major and potentially fatal consequence of antibodies produced against platelet factor 4 ( PF 4)–heparin complexes following heparin exposure. Not all anti‐ PF 4–heparin antibodies are pathogenic, so overdiagnosis can occur, with resulting inappropriate use of alternative anticoagulation therapies that have associated risks of bleeding. However, definitive platelet functional assays are not widely available for routine analysis. Objectives To assess the utility of dimeric recombinant soluble Fcγ RII a (rsFcγ RII a) ectodomains for detecting HIT antibodies. Patients/Methods Plasma from 27 suspected HIT patients were tested for pathogenic anti‐ PF 4–heparin antibodies by binding of a novel dimeric Fcγ RII a ectodomain probe. Plasmas were also tested by the use of PF 4–heparin IgG ELISA , the Hemos IL AcuStar HIT IgG‐specific assay, and a serotonin release assay ( SRA ). Results The dimeric rsFcγ RII a test produced no false positives and excluded four samples that were positive by IgG ELISA . In this small patient cohort, the novel assay correctly assigned 93% of the suspected HIT patients, with two of the HIT patients being scored as false negatives. The improved discrimination of the novel assay over the IgG ELISA , which scored four false positives, supports the mechanistic interpretation that binding of dimeric rsFcγ RII a detects pairs of closely spaced IgG antibodies in PF 4–heparin immune complexes. Conclusions This study found the cell‐free, function‐based dimeric rsFcγ RII a assay to be convenient, simple, and potentially predictive of HIT . The assay had improved specificity over the IgG ELISA , and correlated strongly with the AcuStar HIT IgG‐specific assay, warranting further evaluation of its potential to identify HIT in larger patient cohorts.