Incidence of Heparin Induced Thrombocytopenia (HIT) in patients with severe COVID-19

Abstract Introduction To prevent and treat thrombotic complications in patients hospitalized with severe COVID-19 infection, anticoagulation treatments primarily with heparin and low molecular weight heparin have been recommended. Heparin-induced thrombocytopenia (HIT) is a rare but conceivably fatal reaction to heparin that is characterized by a sudden drop in platelet count accompanied by new onset of thrombosis 4-10 days after heparin exposure. The purpose of this retrospective study was to investigate the prevalence of thrombocytopenia and HIT in hospitalized COVID-19 patients, as well as their association with mortality. Methods 3,672 plasma samples were collected from patients admitted to the first wave of COVID-19 in our institution at New York City (March to May 2020). All patients admitted with a platelet count of less than 150 k/ul were assigned to the thrombocytopenic group. In addition, two groups with similar demographics and normal platelet counts were randomly selected based on discharge outcome: alive vs. deceased (n= 88 per group). PF4 IgG Elisa and heparin neutralization were carried out in accordance with the manufacturer's instructions. A positive HIT result required an optical density (OD) greater than 0.4 and heparin neutralization greater than 50%. Statistical analysis was done in R studio (V.1.4.1717) to analyze demographics (age, gender, ethnicity), initial laboratory data, anticoagulation on admission, and thrombosis. Results Only 86 of the 3,672 (2.3%) patients admitted had thrombocytopenia. Only 1 of the 86 patients tested positive for HIT (1.1% ). 4 cases of the non-survivors (4.5%) tested positive for HIT compared to none of the survivors in the two groups with normal platelet counts. One of these 4 cases had a history of thrombosis (DVT). Interestingly, the PF4 Elisa ODs in non-survivors were significantly higher than in survivors (0.09 vs. 0.06, p-value< 0.001). Although the platelet count did not differ significantly between the two groups, the mean platelet volume (MPV) on admission and its maximum peak during hospitalization were significantly higher in non-survivors than in survivors. Conclusions We only found HIT positive cases among non-survivors, implying that HIT is associated with COVID severity. The incidence of HIT in severe COVID-19 patients appears to be higher than the pre-COVID-19 historical rates of HIT in hospitalized patients (<1%). Although thrombocytopenia is relatively uncommon in COVID-19 patients, the MPV was significantly higher in non-survivors, suggesting that platelet activation and destruction may explain the higher rate of HIT in COVID-19.