Anti-Xa activity below range is related to thrombosis in patients with severe COVID-19.

Objective: We aimed to anlayse the relationship between anti-Xa activity below range and thomboembolic events.

Design: Single center prospective observational longitudinal cohort study (February-November 2021).

Setting: Patients admitted to the ICU of a University Hospital.

Participants: Patients with severe COVID-19 pneumoniae.

Interventions: Enoxaparin was used for prophylactic and therapeutic anticoagulation. Enoxaparin dosing and dose adjustment were based on anti-Xa activity according to the hospital protocol.

Main variables of interest: Target: thomboembolic events.

Predictors: demographics, pharmacotherapy, anti-Xa measurements, clinical data, and laboratory results. Logistic regression was used to identify independent risk factors for thomboembolic events.

Results: Data were available for 896 serum anti-Xa measurements from 228 subjects. Overall, 71.9% were male, with a median age of 62. Most patients needed invasive mechanical ventilation (87.7%) and mortality was 24.1%. A total of 28.9% new thomboembolic events were diagnosed. There were 27.1% anti-Xa measesurements below range. When multivariable logistic regression analysis was performed anti-Xa activity below range (RR, 4.2; p = 0.000), C-reactive protein (25 mg/L increase) (RR, 1.14; p = 0.005) and D-dimer (1000 ng/L increase) (RR, 1.06; p = 0.002) were the independent factors related to new thomboembolic events in patients with severe COVID-19.

Conclusions: Anti-Xa activity below range, C-reactive protein and D-dimer were the independent factors related to thomboembolic events in patients with severe COVID-19. Purposely designed clinical trials should be carried out to confirm the benefit of an anti-Xa monitoring.