Dimeric FcγR ectodomains detect pathogenic anti-platelet factor 4–heparin antibodies in heparin-induced thromobocytopenia

B. D. Wines, C. W. Tan, E. Duncan, S. McRae, R. I. Baker, R. K. Andrews, S. Esparon, E. E. Gardiner, P. M. Hogarth*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    3 Citations (Scopus)


    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 (PF4)–heparin complexes following heparin exposure. Not all anti-PF4–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 FcγRIIa (rsFcγRIIa) ectodomains for detecting HIT antibodies. Patients/Methods Plasma from 27 suspected HIT patients were tested for pathogenic anti-PF4–heparin antibodies by binding of a novel dimeric FcγRIIa ectodomain probe. Plasmas were also tested by the use of PF4–heparin IgG ELISA, the HemosIL AcuStar HIT IgG-specific assay, and a serotonin release assay (SRA). Results The dimeric rsFcγRIIa 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 rsFcγRIIa detects pairs of closely spaced IgG antibodies in PF4–heparin immune complexes. Conclusions This study found the cell-free, function-based dimeric rsFcγRIIa 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.

    Original languageEnglish
    Pages (from-to)2520-2525
    Number of pages6
    JournalJournal of Thrombosis and Haemostasis
    Issue number12
    Publication statusPublished - Dec 2018


    Dive into the research topics of 'Dimeric FcγR ectodomains detect pathogenic anti-platelet factor 4–heparin antibodies in heparin-induced thromobocytopenia'. Together they form a unique fingerprint.

    Cite this