The lungs of patients with COVID-19 show extensive alveolar and interstitial inflammation. SARS-CoV-2 causes lung inflammation which progresses to cytokine storm in the most severe cases. SARS-CoV-2 has an at least 10-fold-greater affinity for human ACE2 than SARS-CoV-1 has. ACE2 is expressed broadly, including in lung alveolar pneumocytes, as well as endothelial cells, the heart, and the kidneys. SARS-CoV-1 and SARS-CoV-2, the enveloped single-stranded RNA viruses responsible for the 2002–2004 SARS epidemic and the more recent COVID-19 pandemic, respectively, bind angiotensin-converting enzyme 2 (ACE2), an intrinsic membrane protein with enzymatic activity that physiologically counters the activation of the renin-angiotensin-aldosterone system. 80% of patients infected by SARS-CoV-2 may be asymptomatic or only mildly symptomatic, but around 10% develop severe respiratory symptoms that evolve to acute respiratory distress syndrome (ARDS). The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) that has swept the globe in 20 causes Coronavirus Disease 2019 (COVID-19), a predominantly respiratory illness with 11.5–13% mortality among hospitalized patients. Here, we review the current state of knowledge of COVID-19 and hemostasis. Disseminated intravascular coagulopathy (DIC) and severe bleeding events are uncommon in COVID-19 patients. COVID-19 patients often have mild thrombocytopenia and appear to have increased platelet consumption, together with a corresponding increase in platelet production. COVID-19 also leads to arterial thrombotic events (including strokes and ischemic limbs) as well as microvascular thrombotic disorders (as frequently documented at autopsy in the pulmonary vascular beds). The degree of D-dimer elevation positively correlates with mortality in COVID-19 patients. This is associated with systemic hypercoagulability and frequent venous thromboembolic events. Initially, COVID-19 infection produces a prominent elevation of fibrinogen and D-dimer/fibrin(ogen) degradation products. Coronavirus disease 2019 (COVID-19) causes a spectrum of disease some patients develop a severe proinflammatory state which can be associated with a unique coagulopathy and procoagulant endothelial phenotype.
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