Among patients diagnosed with coronavirus disease 2019 (COVID-19)-related critical illness without a confirmed or suspected case of venous thromboembolism (VTE), using prophylactic-intensity anticoagulation is suggested over intermediate-intensity anticoagulation, according to new guidelines from the American Society of Hematology (ASH). The recommendation is conditional and is made with low certainty.

Patients diagnosed with COVID-19 who become seriously ill are at a high risk of VTE, which may occur in nearly one-quarter of patients. It is, however, unclear how to best prevent the risk of VTE using thromboprophylaxis in this population of at-risk patients.

Because of the uncertainty of how best to prevent VTEs, there is a high variability in the methods clinicians use, though randomized controlled trials are ongoing. For this guideline update, a panel of experts evaluated the use of intermediate- vs prophylactic-intensity anticoagulation among patients with COVID-19 who are critically ill.

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The guideline update relied on a summary of the currently available evidence. While the experts noted that using intermediate-intensity coagulation may reduce the risk of VTE (odds ratio, 0.93; 95% CI: 0.37-2.32), the overall results are not significant. There is, furthermore, evidence that this modality may increase the risk of all-cause mortality (odds ratio, 1.09; 95% CI: 0.78-1.53), though again these findings were not significant.

These results led the panel to make the following recommendation: “The ASH guideline panel suggests using prophylactic-intensity over intermediate-intensity anticoagulation in patients with COVID-19–related critical illness who do not have suspected or confirmed VTE (conditional recommendation based on low certainty in the evidence about effects.”

They noted, however, that the panel will update these guidelines as more evidence becomes available. The recommendation does not, furthermore, apply to patients in need of anticoagulation for the prevention of thrombosis of extracorporeal circuits.

Further data on how to best predict bleeding events and VTEs in this patient population are also needed.

Disclosure: The study author(s) declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures. 


Cuker A, Tseng EK, Nieuwlaat R, et al. American Society of Hematology living guidelines on the use of anticoagulation for thromboprophylaxis in patients with COVID-19: May 2021 update on the use of intermediate-intensity anticoagulation in critically ill patients. Blood Adv. 2021;5(20):3951-9. doi:10.1182/bloodadvances.2021005493