Enoxaparin dose impacts blood cell phenotypes during mild SARS-CoV-2 infection: the observational single-center study

Coronavirus disease 2019 (COVID-19) is associated with various hemostatic abnormalities requiring constant search for better delicate antithrombotic management in these high-risk patients. The choice and the optimal dose of anticoagulant is important, but unclear, especially for mild COVID-19. Enoxaparin has been tested in several COVID trials with mixed results regarding hard clinical outcomes including mortality. We analyzed clinical, laboratory data and changes in platelets, erythrocytes and leukocytes by scanning electron microscopy on admission and at hospital discharge in patients with confirmed COVID-19 treated with enoxaparin (n = 31) and matched healthy controls (n = 32) in a retrospective observational study. The data were triaged by enoxaparin dose comparing 40 mg/daily prophylactic enoxaparin dose (PED) with 80 mg/daily therapeutic (TED) regimens. All patients experienced mild disease, none required pulmonary support, and all survived. The impact of enoxaparin dose was prominent for platelets and erythrocytes, but less evident for leukocytes. PED was associated with significant platelet activation, diminished numbers of silent nonactive discoid cells, and increased number and size of platelet microaggregates with leukocyte involvement. In contrast, TED did not cause extra platelet activation, while circulating platelet microaggregates were smaller and lacking leukocytes in their construction. PED caused significant increase of erythrocyte-platelet aggregates formation, and numerically higher proportion of circulating echinocytes. TED was associated with significant decrease of rouleaux sludge formation compared to only some trend after PED. Changes in leukocytes were less dependent on enoxaparin dose. However, PED has been associated with enhanced aggregate formation in 7 out of 10 patients, while trap net formation has been decreased in 17 out of 21 TED patients. We conclude that over hospital stay TED was superior to PED in patients with mild COVID-19. The inability of PED to adequately protect major circulating blood cells is probably due to enhanced clearance or/and diminished bioavailability of enoxaparin during COVID. These retrospective observational small sample size data may be relevant to better understanding of the mixed results in controlled outcome-driven trials exploring optimal COVID-19 anticoagulant strategies.