COVID-19 Patients at a Higher Risk of Venous Thromboembolism Compared to Influenza Patients

A new study shows that hospitalized patients with SARS-CoV-2 (COVID-19) are more likely to have venous thromboembolism (VTE) than those with influenza, but chronic anticoagulation use for COVID patients can help mitigate the likelihood of severe respiratory and clinically apparent VTE. The results were published in Thrombosis Research.

COVID-19 is associated with a 21% increased risk of VTE, but the findings of previous studies indicate that chronic anticoagulation at the time of SARS-CoV-2 diagnosis reduced the risk of thrombotic complications. The researchers used influenza as a comparison, because like COVID, flu is associated with substantial rates of hospitalization, respiratory failure, and death. They sought to answer one key question: is chronic anticoagulation at the time of infection beneficial in hospitalized SARS-CoV-2 patients, and if so, is there an apparent benefit for hospitalized influenza?

In this retrospective, single-institution study, researchers assessed 495 patients with a positive COVID-19 PCR testing from March 13, 2020, through September 30, 2020, and 429 patients with a positive Influenza A or B PCR testing from September 2019, through May 2020. They then used electronic medical record (EMR) interrogation confirmed by manual chart review to identify individuals using therapeutic anticoagulation (warfarin, enoxaparin, direct oral anticoagulants [DOAC]) regardless of indication for at least one month before positive PCR testing.  Student’s paired t-test, Mann-Whitney test, or Chi-square were used for analyze data between the groups.

Results Further Highlight the Deadly Nature of COVID-19

According to the results, patients in both cohorts who were taking chronic therapeutic anticoagulation were notably older compared to those not taking chronic anticoagulation. The researchers noted that large age discrepancy likely muted any benefit associated with anticoagulation at the time of infection. Also, in COVID-19 patients, therapeutic anticoagulation was continued for all but eight patients. The researchers observed that COVID-19 patients had more severe illness and an elevated instance of VTE compared to flu patients. However, the results suggest chronically anti-coagulated COVID-19 patients may have had less severe respiratory failure with markedly fewer patients proned, and intubated compared to COVID patients who were not anti-coagulated at the time of diagnosis.
In terms of limitations, because this was an observational retrospective study, it was hard to discern from a retrospective chart review why interventions were pursued or not. The researchers noted that older age and higher incidence of dementia likely influenced treatment decisions and outcomes in the COVID-19 group compared to the influenza patients. A more definitive statement regarding the incidence of VTE would have required a prospective screening approach in both cohorts.
The researchers wrote in conclusion that: “In summary, this retrospective cohort study observed that hospitalized SARS-CoV-2 patients were more likely to have a clinically apparent VTE than those admitted with influenza. Chronic anticoagulation use for SARS-CoV-2 patients was associated with less severe respiratory failure and numerically fewer VTE. Our real world findings complement the recent ACTIV study demonstrating that anticoagulation at the earliest time point may be more beneficial in preventing severe illness,”
They added that: “Further studies are necessary to determine whether the apparent increased rate of VTE is directly related to a unique aspect of the SARS-CoV-2 infection or more generally to the apparently increased severity of illness.”