Measurement of procoagulant platelets provides mechanistic insight and diagnostic potential in heparin‐induced thrombocytopenia

Abstract

Background Heparin‐induced thrombocytopenia (HIT) is a prothrombotic, immune‐mediated adverse drug reaction associated with high rates of thrombosis‐related morbidity and mortality caused by FcγRIIa‐activating pathogenic antibodies to PF4‐heparin. Procoagulant platelets are a platelet subset that promote thrombin generation, are clinically relevant in prothrombotic diseases, and are formed when platelet G‐protein‐coupled receptor (GPCR) and ITAM‐linked receptors are co‐stimulated. Objectives We examined the procoagulant platelet response of healthy donors to platelet agonists in the presence of HIT plasma and determined the contribution of FcγRIIa. Patients/Methods Our previously established flow cytometry‐based procoagulant platelet assay was modified to incorporate plasma samples, performed using FcγRIIa‐responsive donor platelets. Plasma samples were serotonin‐release assay–confirmed HIT (HIT+), or negative on HIT screening. Results In response to GPCR stimulation, only HIT+ plasma produced a heparin‐dependent sensitization that required active FcγRIIa. As a potential diagnostic tool, the procoagulant platelet assay achieved 98% accuracy in identifying clinically verified HIT when performed blinded to the diagnoses of a validation cohort. Samples inducing a higher procoagulant platelet response were more likely from patients with thrombotic complications. Thrombin stimulation markedly increased the procoagulant platelet response with HIT+ plasma that was heparin independent and only partially reversed by FcγRIIa blockade, possibly reflecting ongoing thrombotic risk after heparin cessation. Conclusions We demonstrate that HIT plasma together with platelet agonists increased the procoagulant platelet proportions, which may contribute to thrombotic risk in HIT. Targeting procoagulant platelet activation may represent a novel treatment strategy. This assay may be a rapid, clinically relevant functional assay for accurately detecting pathological HIT antibodies. Show more