Antithrombin Activity Is Associated with Persistent Thromboinflammation and Mortality in Patients with Severe COVID-19 Illness

Introduction: Severe COVID-19 illness can lead to thrombotic complications, organ failure, and death. Antithrombin (AT) regulates thromboinflammation and is a key component of chemical thromboprophylaxis. Our goal was to examine the link between AT activity and responsiveness to thromboprophylaxis, markers of hypercoagulability, and inflammation among severe COVID-19 patients. Methods: This was a single-center, prospective observational study enrolling SARS-CoV-2-positive patients admitted to the intensive care unit on prophylactic enoxaparin. Blood was collected daily for 7 days to assess AT activity and anti-factor Xa levels. Patient demographics, outcomes, and hospital laboratory results were collected. Continuous variables were compared using Mann-Whitney tests, and categorical variables were compared using χ2 tests. Multivariable logistic regression was used to determine the association between AT activity and mortality. Results: In 36 patients, 3 thromboembolic events occurred, and 18 (50%) patients died. Patients who died had higher fibrinogen, D-dimer, and C-reactive protein (CRP) levels and lower AT activity. Reduced AT activity was independently associated with mortality and correlated with both markers of hypercoagulability (D-dimer) and inflammation (CRP). Conclusion: Low AT activity is associated with mortality and persistent hypercoagulable and proinflammatory states in severe COVID-19 patients. The anti-thromboinflammatory properties of AT make it an appealing therapeutic target for future studies.