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How Common Is Venous Thromboembolism in Patients Hospitalized With COVID-19?

December 30, 2021

Reports have suggested that venous thromboembolism (VTE) is a frequent complication of COVID-19 infection, and patients are at an increased thrombotic risk even with prophylactic anticoagulation, but the reported incidence of VTE varies based on geographic area and disease severity. In a study published in Blood Advances, researchers reviewed electronic health record (EHR) data from a large academic health system to characterize the association between VTE and COVID-19 infection, finding an overall VTE incidence of 3.1% among patients hospitalized with COVID-19. Risk was higher for patients who received mechanical ventilation.

The authors, led by Jason Hill, MD, of the University of Queensland Ochsner Clinical School in New Orleans, also noted, "Although our overall rate of VTE in hospitalized patients was low, half of our cases occurred in patients who were receiving effective VTE prophylaxis prior to their VTE." Still, they concluded that a traditional primary VTE prevention approach is sufficient for patients with COVID-19, at least until more widescale and longer-term investigations are performed.

For this study, Dr. Hill and coauthors performed a retrospective review of EHR data obtained from Ochsner Health, a large New Orleans-based academic health care system. The analysis included records from 6,153 patients with PCR-confirmed COVID-19 infection who were admitted to the hospital or treated and discharged from an emergency department (ED) between March 1 and May 1, 2020.

Of these patients, 2,748 were admitted to the hospital and 3,405 received care only through an ED. A total of 637 patients required mechanical ventilation and 206 required renal replacement therapy.

There were 86 total VTE events diagnosed during hospital stay and an additional 3 VTEs diagnosed in the ED, for an incidence rate of 3.1%. Among the 86 patients who developed a VTE during hospital stay, 84 had received thromboprophylaxis. The 2 patients who did not receive thromboprophylaxis were considered at low risk for VTE, as determined by Padua prediction score. Pharmacologic prophylaxis included low-dose low-molecular-weight heparin or unfractionated heparin. Patients with a contraindication for medical anticoagulant therapy received mechanical prophylaxis with elastic compression stockings or sequential compression devices.

Most of the inpatient VTE events were deep vein thrombosis (DVT; 48%), and 40.6% were diagnosed as pulmonary embolism. The remaining VTE cases did not have confirmatory studies available and were deemed to have VTE based on clinical impression of the care team. Three patients experienced VTE after discharge (0.1%), on or before May 21.

Most of the patients who had a VTE had a "high risk" Padua score of ≥4 (n=77; 89%); of this group, 74 experienced VTE during their hospital stay, and 4 experienced a post-discharge VTE.

One-half of the patients with new VTE during inpatient stay (n=43) met the criteria for "prophylaxis failure," defined as any DVT or pulmonary embolism event diagnosed ≥3 days after the admission of a patient who had received ≥2 days of evidence-based mechanical or pharmacologic VTE prophylaxis immediately prior. This group included:

  • 7 patients who received mechanical prophylaxis only
  • 4 who received unfractionated heparin
  • 5 who received only low-molecular-weight heparin
  • 27 patients who received a combination of mechanical and pharmacologic prophylaxis

VTE incidence was substantially higher in the subgroup of patients with COVID-19 who needed mechanical ventilation during the hospital stay, at 7.1% (n=45/637), the authors reported. However, "our observation that VTE occurred in less than 10% of patients requiring mechanical ventilation (the vast majority of whom were probably receiving effective VTE prophylaxis) suggests that the prophylaxis ‘failure rate' among very sick patients with COVID-19 may not be dramatically different from what has been previously described in other critically ill populations," they noted.

In the hospitalized group, 2,075 patients survived to be discharged, for a mortality rate of 24.5%. The mortality rate appeared to be slightly higher among patients diagnosed with a VTE, the researchers added, at 28% (n=24/86).

Limitations of this study included its retrospective nature, particularly the EHR query strategy, which the researchers suggest may have missed some VTE cases. In addition, the study's search strategy was not designed to capture VTE events beyond May 21, especially those that were fatal or did not require medical attention. The researchers noted that many of the patients in this study are still at risk of VTE, and longer-term follow-up may be necessary to identify future VTE events.

"Until additional prospective outcome data are reported, and underlying mechanisms are better understood," the researchers concluded, "our findings support a traditional approach to VTE prophylaxis, both during and after hospitalization, for patients with COVID-19." However, the rate of prophylaxis failure indicates that traditional approach to VTE prophylaxis may be inadequate for some patients with COVID-19.

The authors report no relevant conflicts of interest.


Hill J, Garcia D, Crowther M, et al. Frequency of venous thromboembolism in 6,513 patients with COVID-19: A retrospective study. Blood Adv. November 2, 2020.


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