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Coronavirus disease 2019 (COVID-19) is a highly prothrombotic viral infection that primarily manifests as an acute respiratory syndrome. However, critically ill COVID-19 patients will often develop venous thromboembolism with associated increases in morbidity and mortality. The cause for this prothrombotic state is unclear but is likely related to platelet hyperactivation. In this review, we summarize the current evidence surrounding COVID-19 thrombosis and platelet hyperactivation. We highlight the fact that several studies have identified a soluble factor in COVID-19 patient plasma that is capable of altering platelet phenotype in vitro . Furthermore, this soluble factor appears to be an immune complex, which may be composed of COVID-19 Spike protein and related antibodies. We suggest that these Spike-specific immune complexes contribute to COVID-19 platelet activation and thrombosis in a manner similar to heparin-induced thrombocytopenia. Understanding this underlying pathobiology will be critical for advancement of future research and therapeutic options., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Jevtic and Nazy.)

Background: Coronavirus disease 2019 (COVID-19) occurs following infection with the potentially fatal, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus. Infection can be complicated by coagulopathy, at times featuring thrombocytopenia and thrombosis alongside other coagulation abnormalities, also termed COVID-19-associated coagulopathy (CAC). Data concerning CAC in pregnancy are limited. Better understanding of physician experiences is essential to identify current practice patterns and knowledge gaps., Objectives: To determine physician experiences and practice patterns regarding CAC in pregnancy., Methods: Self-administered survey using the RedCap online platform; supported by the ISTH Subcommittee on Women's Health Issues in Thrombosis and Hemostasis., Results: Seventy-five respondents fully or partially completed the survey. Of 1546 reported cases, disease severity was specified in 1298. Sixty-four percent of COVID-19 infections were mild, whereas 4% were severe. Of all cases, 1% developed CAC, with 65% classified as severe. The most frequent abnormalities included thrombocytopenia, elevated C-reactive protein, D-dimer, and lymphopenia. Low molecular weight heparin was the anticoagulant of choice in CAC and was provided by 77% of respondents, with 60% using standard prophylactic dosing. Thrombosis occurred in seven anticoagulated patients who were receiving standard prophylactic (four) or weight-based (three) dosing. Disease severity and additional thrombosis risk factors dictated anticoagulation duration., Conclusion: In the select population reported by our survey, CAC appears to be uncommon in pregnancy. Anticoagulation practices vary and may not reflect current guidelines. Venous thromboembolism was observed in some CAC patients despite prophylactic anticoagulation (including standard and weight-adjusted dosing). Urgent research is required to determine appropriate anticoagulant dosing and duration in pregnant women with COVID-19 infection., (© 2021 International Society on Thrombosis and Haemostasis.)

Background: Thrombocytopenia and thrombosis are prominent in coronavirus disease 2019 (COVID-19), particularly among critically ill patients; however, the mechanism is unclear. Such critically ill COVID-19 patients may be suspected of heparin-induced thrombocytopenia (HIT), given similar clinical features., Objectives: We investigated the presence of platelet-activating anti-platelet-factor 4 (PF4)/heparin antibodies in critically ill COVID-19 patients suspected of HIT., Patients/methods: We tested 10 critically ill COVID-19 patients suspected of HIT for anti-PF4/heparin antibodies and functional platelet activation in the serotonin release assay (SRA). Anti-human CD32 antibody (IV.3) was added to the SRA to confirm FcγRIIA involvement. Additionally, SARS-CoV-2 antibodies were measured using an in-house ELISA. Finally, von Willebrand factor (VWF) antigen and activity were measured along with A Disintegrin And Metalloprotease with ThromboSpondin-13 Domain (ADAMTS13) activity and the presence of anti-ADAMTS13 antibodies., Results: Heparin-induced thrombocytopenia was excluded in all samples based on anti-PF4/heparin antibody and SRA results. Notably, six COVID-19 patients demonstrated platelet activation by the SRA that was inhibited by FcγRIIA receptor blockade, confirming an immune complex (IC)-mediated reaction. Platelet activation was independent of heparin but inhibited by both therapeutic and high dose heparin. All six samples were positive for antibodies targeting the receptor binding domain (RBD) or the spike protein of the SARS-CoV-2 virus. These samples also featured significantly increased VWF antigen and activity, which was not statistically different from the four COVID-19 samples without platelet activation. ADAMTS13 activity was not severely reduced, and ADAMTS13 inhibitors were not present, thus ruling out a primary thrombotic microangiopathy., Conclusions: Our study identifies platelet-activating ICs as a novel mechanism that contributes to critically ill COVID-19., (© 2021 International Society on Thrombosis and Haemostasis.)