Heparin induced thrombocytopenia in relation to SARS-CoV-2 infection and ABO blood group

Abstract

•This study, prior to SARS-CoV-2 vaccination in Canada, included 2,739,676 adults.•Among 38 individuals with HIT, all had a negative SARS-CoV-2 test.•HIT risk was unrelated to O blood group, before or during the pandemic.•It is unlikely that a component of the SARS-CoV-2 viral particle triggers HIT. Since late 2020, a rare prothrombotic thrombocytopenic condition has been observed to arise within 5 to 30 days after vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [[1]Greinacher A. Thiele T. Warkentin T.E. Weisser K. Kyrle P.A. Eichinger S. Thrombotic thrombocytopenia after ChAdOx1 nCov-19 vaccination.N. Engl. J. Med. 2021 Apr 9; https://doi.org/10.1056/NEJMoa2104840Crossref PubMed Scopus (1220) Google Scholar]. This condition – called “Vaccine Induced Immune Thrombotic Thrombocytopenia” (VITT) – has many similarities to an atypical variant of heparin-induced thrombocytopenia, including unusual sites for VTE, in addition to positive platelet-activating antibodies against platelet factor 4 (PF4) [[2]Scully M. Singh D. Lown R. Poles A. Solomon T. Levi M. et al.Pathologic antibodies to platelet factor 4 after ChAdOx1 nCoV-19 vaccination.N. Engl. J. Med. 2021 Apr 16; https://doi.org/10.1056/NEJMoa2105385Crossref PubMed Scopus (569) Google Scholar]. Prior to SARS-CoV-2, “spontaneous HIT” was described in the absence of proximate exposure to heparin [[3]Greinacher A. Selleng K. Warkentin T.E. Autoimmune heparin-induced thrombocytopenia.J. Thromb. Haemost. 2017; 15: 2099-2114https://doi.org/10.1111/jth.13813Crossref PubMed Scopus (240) Google Scholar]. While the mechanism for the VITT immune response is unclear, preliminary data suggest that an antigen constituent specific to the ChAdOx1 nCoV-19 vaccine may bind to PF4 – rendering it antigenic – and set off a proinflammatory reaction that increases the likelihood of forming anti-PF4 antibodies [[4]A Greinacher K Selleng J Wesche S Handtke R Palankar K Aurich , et al. Towards Understanding ChAdOx1 nCov-19 Vaccine-induced Immune Thrombotic Thrombocytopenia (VITT). 10.21203/rs.3.rs-440461/v1.Google Scholar]. Even so, it remains possible that something inherently related to SARS-CoV-2 viral particle itself, such as the spike protein antigen, may trigger VITT: Persons with COVID-19 disease display a unique coagulopathy [[5]Iba T. Levy J.H. Connors J.M. Warkentin T.E. Thachil J. Levi M. The unique characteristics of COVID-19 coagulopathy.Crit. Care. 2020; 24: 360https://doi.org/10.1186/s13054-020-03077-0Crossref PubMed Scopus (258) Google Scholar], and an aggressive tendency for thrombosis [6Ray J.G. Vermeulen M.J. Schull M.J. Park A.L. ABO Blood Group, SARS-CoV-2 infection, and risk of venous thromboembolism: population-based cohort study.Clin. Appl. Thromb. Hemost. 2021 Jan-Dec; 27 (PMID: 33827287)10760296211008986https://doi.org/10.1177/10760296211008986Crossref Scopus (3) Google Scholar, 7Baldini T. Asioli G.M. Romoli M. Carvalho Dias M. Schulte E.C. Hauer L. Cerebral venous thrombosis and severe acute respiratory syndrome coronavirus-2 infection: a systematic review and meta-analysis.Eur. J. Neurol. 2021 Jan 11; (doi: 10.1111/ene.14727)https://doi.org/10.1111/ene.14727Crossref PubMed Scopus (61) Google Scholar]. Of note, those with blood group O appear somewhat protected against SARS-CoV-2 infection [8Ray J.G. Schull M.J. Vermeulen M.J. Park A.L. Association between ABO and Rh blood groups and SARS-CoV-2 infection or severe COVID-19 illness: a population-based cohort study.Ann. Intern. Med. 2021; 174: 308-315https://doi.org/10.7326/M20-4511Crossref PubMed Scopus (84) Google Scholar, 9Ellinghaus D. Degenhardt F. Bujanda L. et al.Genomewide association study of severe Covid-19 with respiratory failure.NEJM. 2020; https://doi.org/10.1056/NEJMoa2020283Crossref PubMed Scopus (1023) Google Scholar], and distinctly, have a lower risk of VTE than non-O blood groups [6Ray J.G. Vermeulen M.J. Schull M.J. Park A.L. ABO Blood Group, SARS-CoV-2 infection, and risk of venous thromboembolism: population-based cohort study.Clin. Appl. Thromb. Hemost. 2021 Jan-Dec; 27 (PMID: 33827287)10760296211008986https://doi.org/10.1177/10760296211008986Crossref Scopus (3) Google Scholar, 10Wu O. Bayoumi N. Vickers M.A. Clark P. ABO(H) blood groups and vascular disease: a systematic review and meta-analysis.J. Thromb. Haemost. 2008; 6: 62-69https://doi.org/10.1111/j.1538-7836.2007.02818.xCrossref PubMed Scopus (302) Google Scholar]. Survivors of COVID-19 with B blood group display higher neutralizing antibodies against SARS-CoV-2 than survivors with blood group O [[11]Bloch E.M. Patel E.U. Marshall C. Littlefield K. Goel R. Grossman B.J. et al.ABO blood group and SARS-CoV-2 antibody response in a convalescent donor population.Vox Sang. 2021; https://doi.org/10.1111/vox.13070Crossref Scopus (15) Google Scholar]. No data have been published about whether the risk of HIT changed during the SARS-CoV-2 pandemic, or whether ABO blood group modulates that risk. The current study was completed prior to the start of SARS-CoV-2 vaccination in Canada. Its goals were to evaluate the risk of a positive HIT screening assay in relation to the SARS-CoV-2 pandemic, and then compare the risk of a positive HIT screening assay +/− thrombosis by ABO blood group, both before, and during, the SARS-CoV-2 pandemic. This population-based retrospective cohort study was conducted in the province of Ontario, Canada, where there is universal health care. We used patient-level datasets for all of Ontario, which were linked using unique encoded identifiers and analyzed at ICES. Laboratory testing for HIT antibodies, ABO blood group and SARS-CoV-2 is from the Ontario Lab Information System (OLIS), as described elsewhere [6Ray J.G. Vermeulen M.J. Schull M.J. Park A.L. ABO Blood Group, SARS-CoV-2 infection, and risk of venous thromboembolism: population-based cohort study.Clin. Appl. Thromb. Hemost. 2021 Jan-Dec; 27 (PMID: 33827287)10760296211008986https://doi.org/10.1177/10760296211008986Crossref Scopus (3) Google Scholar, 8Ray J.G. Schull M.J. Vermeulen M.J. Park A.L. Association between ABO and Rh blood groups and SARS-CoV-2 infection or severe COVID-19 illness: a population-based cohort study.Ann. Intern. Med. 2021; 174: 308-315https://doi.org/10.7326/M20-4511Crossref PubMed Scopus (84) Google Scholar]. Included were Ontario residents with an ABO blood group laboratory result in OLIS between January 2007 and September 2020. Study entry started at April 1, 2007 (the first available date for HIT laboratory data in OLIS) or the date at which the individual turned age 16, whichever was later. The exposures of interest were (i) pre-SARS-COV-2 era (April 1, 2007 to December 31, 2019), vs. the pandemic period (January 1, 2020 to September 30, 2020 – which preceded the initiation of SARS-CoV-2 vaccination); (ii) SARS-CoV-2 infection, namely, those who tested positive for SARS-CoV-2 by viral RNA PCR testing; and (iii) ABO blood group. The SARS-CoV-2 test date was that on which the SARS-CoV-2 specimen was collected. For a given individual, if more than one positive specimen date was available, then the earliest positive specimen was considered; otherwise the earliest negative specimen was considered. The main study outcome was a positive HIT screening assay, defined by a positive highly-sensitive enzyme-linked immunosorbent assay (ESLIA) or latex-enhanced immunoassay for anti-PF4/polyanion antibodies. Weakly positive tests were considered as negative. A second outcome was a positive HIT screening assay with VTE diagnosed within +/− 30 days of the HIT specimen. The determination of pulmonary embolism (PE) or deep vein thrombosis (DVT) required a coded diagnosis of either condition, in conjunction with the performance of objective imaging [6Ray J.G. Vermeulen M.J. Schull M.J. Park A.L. ABO Blood Group, SARS-CoV-2 infection, and risk of venous thromboembolism: population-based cohort study.Clin. Appl. Thromb. Hemost. 2021 Jan-Dec; 27 (PMID: 33827287)10760296211008986https://doi.org/10.1177/10760296211008986Crossref Scopus (3) Google Scholar, 8Ray J.G. Schull M.J. Vermeulen M.J. Park A.L. Association between ABO and Rh blood groups and SARS-CoV-2 infection or severe COVID-19 illness: a population-based cohort study.Ann. Intern. Med. 2021; 174: 308-315https://doi.org/10.7326/M20-4511Crossref PubMed Scopus (84) Google Scholar]. Cox proportional hazard models generated adjusted hazard ratios (aHR) and 95% CI. In the first two models, the risk for a positive HIT screening assay, as well as for a positive HIT screening assay with VTE, was compared between the pre-pandemic period (April 2007 to December 2019) vs. the SARS-CoV-2 pandemic (January 2020 to September 2020). In the next two models, the aHR for a positive HIT screening assay, and a positive HIT screening assay with VTE, were each calculated comparing persons with O vs. non-O blood groups. 2,739,676 persons were included. The mean (SD) age was 39.0 (19.0) years, 856,093 (31.2%) were male, and 35.7% were blood group A, 5.0% AB, 16.1% B ad 43.2% O. 833 persons had a positive HIT screening assay (30.4 per 100,000 persons) in the whole study period, at a mean age of 65.3 (14.5) years; 192 had a positive HIT screening assay with VTE (7.0 per 100,000 persons). The rate of a positive HIT screening assay was higher during the pandemic than prior to its onset (aHR 1.45, 95% CI 1.13 to 1.85) (Table 1). For a positive HIT screening assay with VTE, the corresponding aHR was 1.46 (95% CI 0.88 to 2.44) (Table 1). As HIT testing or test availability may have changed over time, a post hoc analysis restricted the pre-pandemic era to January 2016 to December 2019, revealing 469 cases of a positive HIT screening assay therein (4.5 per 100,000 person-years) – an aHR of 0.82 (95% CI 0.64 to 1.05); as well as 107 cases of a positive HIT screening assay with VTE (1.1 per 100,000) – an aHR of 0.82 (95% CI 0.49 to 1.39).Table 1Positive heparin-induced thrombocytopenia (HIT) screening assay, or positive HIT screening assay with venous thromboembolism (VTE), before (April 2007 to December 2019) and after (January 2020 to September 2020) the onset of the SARS-CoV-2 pandemic.OutcomePerson-years of follow-upNo. with outcome (incidence rate per 100,000 person-years)Hazard ratio (95% CI)UnadjustedAdjustedbAdjusted for sex and year at study entry.Positive HIT screening assayBefore SARS-CoV-2 pandemic (N = 2,731,362)aSome individuals contribute follow-up time during both eras.30,781,632764 (2.5)1.00 (referent)1.00 (referent)During SARS-CoV-2 pandemic (N = 2,479,996)aSome individuals contribute follow-up time during both eras.1,835,71469 (3.8)1.47 (1.15 to 1.88)1.45 (1.13 to 1.85)Positive HIT screening assay with VTEBefore SARS-CoV-2 pandemic (N = 2,731,362)aSome individuals contribute follow-up time during both eras.30,782,671176 (0.57)1.00 (referent)1.00 (referent)During SARS-CoV-2 pandemic (N = 2,480,258)aSome individuals contribute follow-up time during both eras.1,835,91516 (0.87)1.45 (0.88 to 2.42)1.46 (0.88 to 2.44)a Some individuals contribute follow-up time during both eras.b Adjusted for sex and year at study entry. Open table in a new tab Among the entire cohort of 2,739,676 adults, 557,726 underwent SARS-CoV-2 PCR testing at some time during the current pandemic in Ontario, of which 12,075 (2.2%) tested positive for SARS-CoV-2. In a second post hoc analysis, there were 38 individuals who had a positive HIT screening assay within 7 days before, or any time after, their SARS-CoV-2 PCR test. In each case, SARS-CoV-2 PCR testing was negative, precluding any formal statistical modelling. Across all era, no significant association was observed between O vs. non-O blood group and the risk of a positive HIT screening assay (Fig. 1, upper red). A similar lack of association was seen for blood group and the outcome of a positive HIT screening assay with VTE (Fig. 1, lower blue). As there were no prior data about ABO blood group, or SARS-CoV-2, and the risk of A POSITIVE HIT SCREENING ASSAY, it is unlikely that clinical knowledge of a person's blood group or their SARS-CoV-2 test status would have influenced HIT testing. Nevertheless, the threshold for HIT testing may have been lowered during the pandemic, as patients afflicted with COVID-19 severe disease are popularly known to experience thrombocytopenia [[12]Chen W. Li Z. Yang B. Wang P. Zhou Q. Zhang Z. et al.Delayed-phase thrombocytopenia in patients with coronavirus disease 2019 (COVID-19).Br. J. Haematol. 2020; 190: 179-184https://doi.org/10.1111/bjh.16885Crossref PubMed Scopus (39) Google Scholar] and VTE [6Ray J.G. Vermeulen M.J. Schull M.J. Park A.L. ABO Blood Group, SARS-CoV-2 infection, and risk of venous thromboembolism: population-based cohort study.Clin. Appl. Thromb. Hemost. 2021 Jan-Dec; 27 (PMID: 33827287)10760296211008986https://doi.org/10.1177/10760296211008986Crossref Scopus (3) Google Scholar, 7Baldini T. Asioli G.M. Romoli M. Carvalho Dias M. Schulte E.C. Hauer L. Cerebral venous thrombosis and severe acute respiratory syndrome coronavirus-2 infection: a systematic review and meta-analysis.Eur. J. Neurol. 2021 Jan 11; (doi: 10.1111/ene.14727)https://doi.org/10.1111/ene.14727Crossref PubMed Scopus (61) Google Scholar], and Canadian directives recommended pharmacological VTE prophylaxis in COVID-19 ill patients [[13]Bresee L. MacDougall D. Venous thromboembolism prophylaxis in patients hospitalized with COVID-19. CADTH, Ottawa2020 Junehttps://cadth.ca/sites/default/files/covid-19/eh0086-vte-prophylaxis-in-covid19-final.pdfGoogle Scholar]. The HIT ELISA and latex-enhanced immunoassay are highly sensitive, but less specific, for the detection of HIT; yet, confirmatory testing with the more specific serotonin release assay (SRA) [[14]Warkentin T.E. Sheppard J.A.I. Testing for heparin-induced thrombocytopenia antibodies.Trans. Med. Rev. 2006; 20: 259-272Crossref PubMed Scopus (107) Google Scholar] was not performed herein. It is, therefore, not known, how many patients in the study were really HIT patients. Use of heparin-based thromboprophylaxis or treatments was also not known. Accordingly, the apparent rise in a positive HIT screening assay during the SARS-CoV-2 era may be an epiphenomenon [[15]May J.E. Siniard R.C. Marques M. The challenges of diagnosing heparin-induced thrombocytopenia in patients with COVID-19.Res. Pract. Thromb. Haemost. 2020; 4: 1066-1067https://doi.org/10.1002/rth2.12416Crossref Scopus (10) Google Scholar], especially since no individuals herein were positive for SARS-CoV-2 infection among the 38 who had a positive HIT screen around the time of their SARS-CoV-2 PCR test. It is possible that a minority of persons with COVID-19 severe disease and HIT, including fatal VTE, may have died prior to arriving to hospital for SARS-CoV-2 testing. Even so, one would have expected to identify most events among those who were hospitalized. If SARS-CoV-2 related HIT is as rare as VITT following vaccination, then we may have failed to detect those cases, despite the large study sample size. Importantly, the current study was completed prior to the introduction of SARS-CoV-2 vaccination in Canada, precluding cases of VITT that might otherwise be confused with HIT. No peer-reviewed data exist about ABO blood group and HIT. One preliminary abstract reported a significant association between a common variant in the ABO gene and SRA-confirmed HIT (odds ratio [OR] 0.39, 95% CI 0.17 to 0.89), with O blood group being associated with a higher odds of HIT (OR 1.42, 95% CI 1.25 to 1.61) [[16]Giles J.B. Rollin J. Shaffer C.M. Steiner H.E. Momozawa Y. Stanaway I. et al.Genome-wide association study identifies variation in ABO as risk factor for platelet reactivity in heparin-induced thrombocytopenia.Blood. 2020; 136: 38-39https://doi.org/10.1182/blood-2020-139651Crossref Google Scholar]. While we observed no such association, our determination of ABO status was only based on conventional testing using antibodies against type A and B blood. The existing body of evidence suggests that O blood group may be protective against SARS-CoV-2 infection and COVID-19 severe illness [8Ray J.G. Schull M.J. Vermeulen M.J. Park A.L. Association between ABO and Rh blood groups and SARS-CoV-2 infection or severe COVID-19 illness: a population-based cohort study.Ann. Intern. Med. 2021; 174: 308-315https://doi.org/10.7326/M20-4511Crossref PubMed Scopus (84) Google Scholar, 17Golinelli D. Boetto E. Maietti E. Fantini M.P. The association between ABO blood group and SARS-CoV-2 infection: a meta-analysis.PLoS One. 2020; 15e0239508https://doi.org/10.1371/journal.pone.0239508Crossref PubMed Scopus (65) Google Scholar]. One explanation is that the anti-A and anti-B antibodies that determine blood group O may also aid in neutralizing viral particles [[18]Pendu J.L. Breiman A. Rocher J. Dion M. Ruvoën-Clouet N. ABO blood types and COVID-19: spurious, anecdotal, or truly important relationships? A reasoned review of available data.Viruses. 2021; 13: 160https://doi.org/10.3390/v13020160Crossref PubMed Scopus (39) Google Scholar]. While SARS-CoV-2 severe infection is certainly associated with VTE [6Ray J.G. Vermeulen M.J. Schull M.J. Park A.L. ABO Blood Group, SARS-CoV-2 infection, and risk of venous thromboembolism: population-based cohort study.Clin. Appl. Thromb. Hemost. 2021 Jan-Dec; 27 (PMID: 33827287)10760296211008986https://doi.org/10.1177/10760296211008986Crossref Scopus (3) Google Scholar, 7Baldini T. Asioli G.M. Romoli M. Carvalho Dias M. Schulte E.C. Hauer L. Cerebral venous thrombosis and severe acute respiratory syndrome coronavirus-2 infection: a systematic review and meta-analysis.Eur. J. Neurol. 2021 Jan 11; (doi: 10.1111/ene.14727)https://doi.org/10.1111/ene.14727Crossref PubMed Scopus (61) Google Scholar], our current findings do not suggest that the latter is mediated by a HIT-like or ABO blood group antibody response. Understanding the mechanism(s) for VITT is paramount for directing vaccination efforts and minimizing adverse reactions to the vaccine. The current study findings suggest that it is unlikely that something inherently related to SARS-CoV-2 viral particle acts as a trigger for HIT, nor is it apparent that ABO blood group modulates the risk of HIT. If VITT shares a common pathogenesis with HIT – something not yet fully elucidated – then the current study findings indirectly support an alternative cause of VITT, other than the presence of SARS-CoV-2 viral mRNA (or some other SARS-CoV-2 antigen, such as the spike protein) within the vaccine. Emerging data suggest that VITT is potentially mediated by the adenoviral vector used in the ChAdOx1 nCoV-19 [[1]Greinacher A. Thiele T. Warkentin T.E. Weisser K. Kyrle P.A. Eichinger S. Thrombotic thrombocytopenia after ChAdOx1 nCov-19 vaccination.N. Engl. J. Med. 2021 Apr 9; https://doi.org/10.1056/NEJMoa2104840Crossref PubMed Scopus (1220) Google Scholar] and Ad26.COV2.S [[19]See I. Su J.R. Lale A. Woo E.J. Guh A.Y. Shimabukuro T.T. US case reports of cerebral venous sinus thrombosis with thrombocytopenia after Ad26.COV2.S vaccination, March 2 to April 21, 2021.JAMA. 2021 Apr 30; https://doi.org/10.1001/jama.2021.7517Crossref PubMed Scopus (302) Google Scholar] vaccines. Ongoing efforts to document VITT cases might consider whether ABO blood group modulates their tendency to develop the condition. The response to the vaccine in previously SARS-CoV-2 infected persons might also be of value.