Table I.

Thromboemblic risk assessment, monitoring and antithrombotic strategies in COVID-19 patients

Assessment of thromboembolic risk	In all hospitalised patients with COVID-19, taking into account body mass index, individual risk factors for VTE, and the severity of the illness (SOFA score, need for oxygen treatment, mechanical ventilation). Patients at highest risk are those with additional non-modifiable risk factors (i.e., cancer or chronic comorbidities), previous VTE or severe illness (SOFA score ≥4, severe hypoxia, ADRS).
Laboratory monitoring	Platelet count, PT, APTT, fibrinogen and D-dimer, at least every 2–3 days. Useful to assess bleeding risk and surveillance for DIC, to be considered particularly if clinical conditions deteriorate. In patients with sudden and/or marked increase of D-dimer, possible VTE should be investigated.
Thromboprophylaxis	Advised in all patients, with at least standard doses of LMWH, UFH or fondaparinux, unless contraindicated (active bleeding, known bleeding disorders, platelet count <25×109/L). In patients at highest risk, LMWH at adjusted doses is suggested, taking into account the concomitant bleeding risk: enoxaparin 4,000 IU if body weight <50 kg; 6,000 IU, 50–70 kg; 4,000 IU twice daily, 70–100 kg; 6,000 IU twice daily, >100 kg. Particularly in patients in ICU, LMWH at intermediate doses (70 IU/kg twice daily) or UFH achieving approximately APTT ratio 2.0 or anti-Xa=0.5 IU/mL is suggested, considering the concurrent bleeding risk. In patients with kidney insufficiency, monitoring of anti-Xa activity is suggested, maintaining the upper prophylactic range (anti-Xa=0.4–0.5 IU/mL). As an alternative, UFH could be used with the same anti-Xa levels or APTT ratio approximately 1.5–2.0. Fondaparinux can be used at standard doses (2.5 mg daily) if creatinine clearance is >50 mL/min; at lower dose (1.5 mg daily) in patients with creatinine clearance between 20 and 50 mL/min. Mechanical thromboprophylaxis (elastic socks and intermittent pneumatic compression) can be used in patients at highest risk and should be considered if pharmacological prophylaxis is contraindicated. Extension of thromboprophylaxis at hospital discharge should be advised, according to the individual risk, including active mobilisation and the persistence of inflammatory signs.

ADRS: acute distress respiratory syndrome; APTT: activated partial thromboplastin time; DIC: disseminated intravascular coagulation; ICU: intensive care unit; LMWH: low-molecular weight heparin; PT: prothrombin time; SOFA: sequential organ failure assessment; UFH: unfractionated heparin; VTE: venous thromboembolism.