Venous thromboembolism is rare among non-hospitalized COVID-19 patients

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In a recent study published in the journal JAMA Network Open, researchers in the United States assessed the risk and aimed to identify the independent predictors of venous thromboembolism events in outpatients who had less severe manifestations of coronavirus disease 2019 (COVID-19).

Assessment of the Risk of Venous Thromboembolism in Nonhospitalized Patients With COVID-19Study: Assessment of the Risk of Venous Thromboembolism in Nonhospitalized Patients With COVID-19. Image Credit: MattLphotography / Shutterstock


A substantial number of studies have reported that venous thromboembolism is one of the major complications of severe COVID-19, with patients hospitalized with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 infections being at a higher risk of venous thromboembolism than patients hospitalized for non-COVID-19 diseases. Prophylactic treatment with anticoagulants is thought to be beneficial for patients hospitalized with SARS-CoV-2 infections in preventing venous thromboembolism.

However, a large number of individuals who had SARS-CoV-2 infections experienced mild symptoms and were treated in an outpatient setting, not requiring hospitalization. There have been very few studies that have explored the risk of venous thromboembolism among patients who experienced mild COVID-19 symptoms, and the studies that have examined the subject have reported contradictory results with incidence rates ranging from 1.8 persons per 1000 to 18%. Understanding the true incidence rate of venous thromboembolism among COVID-19 patients is essential to formulate treatment and prevention strategies.

About the study

In the present study, the researchers examined a large cohort of non-hospitalized COVID-19 patients using clinical databases from two healthcare delivery systems to estimate the risk of incident venous thromboembolism complications after COVID-19. The study also analyzed the risk according to patient characteristics, such as a history of venous thromboembolism and age to determine risk factors associated with venous thromboembolism complications after SARS-CoV-2 infections.

The participants were above the age of 18 and enrolled in two integrated healthcare delivery systems in California, United States (U.S.). The data for the analyses were obtained from electronic health records and comprised patient demographic information, health service use information, and records on laboratory test results and pharmacy dispensing.

All laboratory-confirmed cases of COVID-19 between January 2020 and January 2021 were identified based on SARS-CoV-2 polymerase chain reaction (PCR) tests of oropharyngeal and nasopharyngeal swabs. Only those participants who had positive PCR test results but were not hospitalized were included in the study.

The measured outcomes included a diagnosed new event of venous thromboembolism after the index date for a positive SARS-CoV-2 PCR test. Cases of pregnancy-related venous thromboembolism and superficial venous thromboses were excluded. Additionally, only those patients who had a relevant radiologic test such as extremity ultrasonography or computed tomography angiogram were included to ensure that the case was for a new venous thromboembolism event. The confirmed cases were classified as pulmonary embolism that may or may not include concomitant events of deep vein thromboses, lower extremity deep vein thromboses, upper extremity deep vein thromboses, and thromboses of unusual sites such as the retinal vein, splanchnic thromboses, or cerebral venous sinus.

The venous thromboembolism risk was analyzed according to sociodemographic factors such as gender, age, race, and ethnicity. Diagnosed thrombophilia, cancer, and hypercoagulable hematologic conditions were the included venous thromboembolism risk factors. Pharmacy dispensing data on oral anticoagulants and cardiovascular measurements were used for baseline analyses.


The results reported that the overall rate of venous thromboembolism events was 0.26 over 100 person-years, with 292 cases of venous thromboembolism identified across 398,530 COVID-19 outpatients. The risk of venous thromboembolism was the highest during the one month following a COVID-19 diagnosis.

The risk factors for venous thromboembolism following COVID-19 not requiring hospitalization included age (increasing hazard ratio with age), male gender, prior events of venous thromboembolism, thrombophilia, body mass index between 30 and 40 and greater than 40, and inflammatory bowel disease.

The authors believe that while the overall low rate of venous thromboembolism events might not rationalize the risk of bleeding and the increased costs associated with anticoagulant administration, the significantly higher rates of venous thromboembolism events among high-risk groups, such as individuals with a history of venous thromboembolism events (12.44 for every 100 person-years in the first month following a COVID-19 diagnosis) indicate that more intensive approaches to prevent venous thromboembolism events for specific groups should be considered.


Overall, the findings reported that the absolute risk of venous thromboembolism events among COVID-19 patients who were treated in an outpatient setting was low. However, male gender, age above 55 years, history of thrombophilia, and obesity significantly increased the risk of venous thromboembolism events in the one month following a diagnosis of COVID-19.

Journal reference:
Dr. Chinta Sidharthan

Written by

Dr. Chinta Sidharthan

Chinta Sidharthan is a writer based in Bangalore, India. Her academic background is in evolutionary biology and genetics, and she has extensive experience in scientific research, teaching, science writing, and herpetology. Chinta holds a Ph.D. in evolutionary biology from the Indian Institute of Science and is passionate about science education, writing, animals, wildlife, and conservation. For her doctoral research, she explored the origins and diversification of blindsnakes in India, as a part of which she did extensive fieldwork in the jungles of southern India. She has received the Canadian Governor General’s bronze medal and Bangalore University gold medal for academic excellence and published her research in high-impact journals.


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