Elevated TAT in COVID-19 Patients with Normal D-Dimer as a Predictor of Severe Respiratory Failure: A Retrospective Analysis of 797 Patients.

Although previous studies have revealed that elevated D-dimer in the early stage of coronavirus 2019 (COVID-19) indicates pulmonary intravascular coagulation, the state of coagulation/fibrinolysis disorder with normal D-dimer is unknown. The study aimed to investigate how coagulation/fibrinolysis markers affect severe respiratory failure in the early stage of COVID-19. Among 1043 patients with COVID-19, 797 patients were included in our single-center retrospective study. These 797 patients were divided into two groups, the normal D-dimer and elevated D-dimer groups and analyzed for each group. A logistic regression model was fitted for age, sex, body mass index (BMI) ≥ 30 kg/m, fibrinogen ≥ 617 mg/dL, thrombin-antithrombin complex (TAT) ≥ 4.0 ng/mL, and plasmin-alpha2-plasmin inhibitor-complex (PIC) > 0.8 µg/mL. A multivariate analysis of the normal D-dimer group demonstrated that being male and TAT ≥ 4.0 ng/mL significantly affected severe respiratory failure. In a multivariate analysis of the elevated D-dimer group, BMI ≥ 30 kg/m and fibrinogen ≥ 617 mg/dL significantly affected severe respiratory failure. The elevated PIC did not affect severe respiratory failure in any group. Our study demonstrated that hypercoagulation due to SARS-CoV-2 infection may occur even during a normal D-dimer level, causing severe respiratory failure in COVID-19.