The Ways of the Virus: Interactions of Platelets and Red Blood Cells with SARS-CoV-2, and Their Potential Pathophysiological Significance in COVID-19.

The hematological effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are important in COVID-19 pathophysiology. However, the interactions of SARS-CoV-2 with platelets and red blood cells are still poorly understood. There are conflicting data regarding the mechanisms and significance of these interactions. The aim of this review is to put together available data and discuss hypotheses, the known and suspected effects of the virus on these blood cells, their pathophysiological and diagnostic significance, and the potential role of platelets and red blood cells in the virus's transport, propagation, and clearance by the immune system. We pay particular attention to the mutual activation of platelets, the immune system, the endothelium, and blood coagulation and how this changes with the evolution of SARS-CoV-2. There is now convincing evidence that platelets, along with platelet and erythroid precursors (but not mature erythrocytes), are frequently infected by SARS-CoV-2 and functionally changed. The mechanisms of infection of these cells and their role are not yet entirely clear. Still, the changes in platelets and red blood cells in COVID-19 are significantly associated with disease severity and are likely to have prognostic and pathophysiological significance in the development of thrombotic and pulmonary complications.

Integral assays of hemostasis in hospitalized patients with COVID-19 on admission and during heparin thromboprophylaxis.

BACKGROUND: Blood coagulation abnormalities play a major role in COVID-19 pathophysiology. However, the specific details of hypercoagulation and anticoagulation treatment require investigation. The aim of this study was to investigate the status of the coagulation system by means of integral and local clotting assays in COVID-19 patients on admission to the hospital and in hospitalized COVID-19 patients receiving heparin thromboprophylaxis. METHODS: Thrombodynamics (TD), thromboelastography (TEG), and standard clotting assays were performed in 153 COVID-19 patients observed in a hospital setting. All patients receiving treatment, except extracorporeal membrane oxygenation (ECMO) patients (n = 108), were administered therapeutic doses of low molecular weight heparin (LMWH) depending on body weight. The ECMO patients (n = 15) were administered unfractionated heparin (UFH). RESULTS: On admission, the patients (n = 30) had extreme hypercoagulation by all integral assays: TD showed hypercoagulation in ~75% of patients, while TEG showed hypercoagulation in ~50% of patients. The patients receiving treatment showed a significant heparin response based on TD; 77% of measurements were in the hypocoagulation range, 15% were normal, and 8% remained in hypercoagulation. TEG showed less of a response to heparin: 24% of measurements were in the hypocoagulation range, 59% were normal and 17% remained in hypercoagulation. While hypocoagulation is likely due to heparin treatment, remaining in significant hypercoagulation may indicate insufficient anticoagulation for some patients, which is in agreement with our clinical findings. There were 3 study patients with registered thrombosis episodes, and all were outside the target range for TD parameters typical for effective thromboprophylaxis (1 patient was in weak hypocoagulation, atypical for the LMWH dose used, and 2 patients remained in the hypercoagulation range despite therapeutic LMWH doses). CONCLUSION: Patients with COVID-19 have severe hypercoagulation, which persists in some patients receiving anticoagulation treatment, while significant hypocoagulation is observed in others. The data suggest critical issues of hemostasis balance in these patients and indicate the potential importance of integral assays in its control.

Filterability of Erythrocytes in Patients with COVID-19.

For the first time, the influence of COVID-19 on blood microrheology was studied. For this, the method of filtering erythrocytes through filters with pores of 3.5 µm was used. Filterability was shown to significantly decrease with the increasing severity of the patient's condition, as well as with a decrease in the ratio of hemoglobin oxygen saturation to the oxygen fraction in the inhaled air (SpO2/FiO2). The filterability of ≤ 0.65, or its fast decrease during treatment, were indicators of a poor prognosis. Filterability increased significantly with an increase in erythrocyte count, hematocrit and blood concentrations of hemoglobin, albumin, and total protein. The effect of these parameters on the erythrocyte filterability is directly opposite to their effect on blood macrorheology, where they all increase blood viscosity, worsening the erythrocyte deformability. The erythrocyte filterability decreased with increasing oxygen supply rate, especially in patients on mechanical ventilation, apparently not due to the oxygen supplied, but to the deterioration of the patients' condition. Filterability significantly correlates with the C-reactive protein, which indicates that inflammation affects the blood microrheology in the capillaries. Thus, the filterability of erythrocytes is a good tool for studying the severity of the patient's condition and his prognosis in COVID-19.