COVID-19: The crucial role of blood coagulation and fibrinolysis

The overflow of studies in the recent literature on COVID-19 often gives provisional or contradictory results and therefore deserves pauses of reflection and reconsideration. In fact, knowledges of pathophysiology of this new disease are still in development and hence originate discussions and interpretations. Regarding the role of blood coagulation and fibrinolysis, these mechanisms should be considered as crucial especially in severe cases. It is proposed to consider two distinct phenotypes of thrombotic manifestations: the current “thromboembolic type” also occurring in other kinds of sepsis, and the diffuse micro-thrombotic type, prevailing in the lungs but sometimes extending to other organs. Both types can induce severe disease and are potentially lethal. The micro-thrombotic pattern, more specific for COVID-19, results from a massive activation of coagulation strictly coupled with a hyper-intense inflammatory and immune reaction. This results in widespread occlusive thrombotic micro-angiopathy with destruction of alveoli and obstructive neoangiogenesis. The involvement of fibrinolysis, often neglected, confers a double faceted process of activation/inhibition, finally conducive to a fibrinolytic shutdown that reinforces persistence of micro-thrombi. Considering these peculiar mechanisms, it seems evident that both prophylactic and therapeutic effects of current anti-thrombotic drugs cannot be taken for granted and need therefore new specific and rigorous controlled trials.