Table 2. Summary of the 15 studies included in this systematic review and their most important findings regarding deep vein thrombosis (DVT) in COVID-19 patients.

PE: pulmonary embolism

	Lead author	Country	Type of study and population	Findings	Conclusion
1	Mei W et al., 2024 [1]	China	Retrospective cohort study on adult patients admitted to the hospital in China between 2019 and 2023	Venous thromboembolism increased from 2019 to 2022 and reached its highest point during December 2022 and January 2023, when there was more liberty during the pandemic. The thromboembolism number was related to those COVID-19 patients who tested positive. The incidence of DVT in COVID-19 patients was 21% in hospitalized patients.	The number of cases of DVT increased when more people tested positive for COVID-19. There was a 21% incidence of DVT in COVID-19 patients.
2	Koleilat I et al., 2021 [2]	United States of America	Retrospective case-control study with patients admitted to the Montefiore Medical Center between March 1, 2020, and April 10, 2020 (n=135)	The incidence of DVT in COVID-19 patients was 13.3%. There was no difference regarding the need for mechanical ventilation, the ratio of arterial partial pressure of oxygen, the fraction of inspired oxygen, and the rate of acute kidney injury between the COVID-19 patients with DVT and the ones without it. However, there was a significant variation in the levels of D-dimer and fibrinogen; D-dimer in patients with DVT was found to be 18.88 µg/mL and fibrinogen of 501.0 mg/dL, versus those non-DVT that had values of 2.55 µg/mL of D-dimer and 654.5 mg/dL of fibrinogen. DVT occurs in COVID-19 patients, even when they have thromboprophylaxis.	Elevated D-dimer is important in studying DVT in COVID-19 patients. The hypercoagulability in COVID-19 with elevated D-dimer and less elevated fibrinogen leads to a significant risk of DVT, despite thromboprophylaxis.
3	Rali P et al., 2021 [7]	United States of America	Retrospective cohort study on patients admitted to the Temple University Hospital between April 1, 2020, to April 27, 2020 (n=147).	The venous thromboembolism incidence rate of 3.5% in patients admitted due to COVID-19. COVID-19 patients with D-dimer admission levels of more than 1500 ng/mL (P=0.013) or in need of invasive mechanical ventilation should be tested for venous thromboembolism. Fourteen out of 147 patients tested for venous thromboembolism were suffering from acute DVT, which represents 9.5%.	There is an association of DVT with COVID-19. Patients with elevated D-dimer or in need of invasive mechanical ventilation should be tested for venous thromboembolism.
4	Jimenez-Guiu X et al., 2021 [8]	Spain	Prospective cohort study on patients admitted to a Spain hospital during April 2020 (n= 67).	The incidence of lower DVT in COVID-19 patients with intermediate or complete anticoagulation doses was 10.5% and, in patients with prophylactic dosages, 16.2%.	DVT has been found in non-critically ill COVID-19 patients with a significant incidence of 10.5%, and even with a higher prevalence in critically ill patients.
5	Erben Y et al., 2023 [9]	United States of America	Retrospective study based on patients with COVID-19 at the Jacksonville campus of the Mayo Clinic from March 11, 2020, to May 27, 2021 (n=876)	The incidence of DVT/PE in COVID-19 patients was 8.7% (P=0.03). The prevalence of DVT in COVID-19 patients is higher among Black/African American patients, which was shown with a 16.2% incidence in this group.	DVT has an important incidence in COVID-19 patients. Black/African Americans have a higher risk of developing DVT in a COVID-19 infection.
6	Choi J et al., 2020 [10]	United States of America	Retrospective cohort study of COVID-19 patients admitted at the New York-Presbyterian/Weill Cornell Medical Center and New York-Presbyterian/Lower Manhattan Hospital between 3 March 2020 and 15 May 2020 (n= 1739).	Venous thromboembolism was seen in 7% of the COVID-19 patients. A total of 136 venous thromboembolism events occurred, where 79 of them were DVT of the lower extremities and 16 cases were DVT of the upper extremities (a total of 5.46% of DVT). Increased levels of D-dimer were related to a higher prevalence of venous thromboembolism in COVID-19 patients.	D-dimer is associated with the risk of DVT in COVID-19. The incidence of DVT in COVID-19 patients was low.
7	Al-Samkari H et al., 2020 [11]	United States of America	Retrospective study of COVID-19 patients admitted to five partner healthcare institutions on the 8th of April 2020 (n=400)	Elevation of D-dimer, platelet count, C-reactive protein, and erythrocyte sedimentation rate was a predictor of DVT in COVID-19. The incidence of venous thromboembolism in COVID-19 patients was 4.8%. DVT was found in 12 out of the 400 patients, which represents a 3% incidence.	The incidence of DVT in COVID-19 patients was low. Elevated D-dimer is a strong predictor of DVT in COVID-19 patients.
8	Motaganahalli R et al., 2021 [12]	United States of America	Retrospective cohort study on COVID-19 patients admitted to the Indiana University Academic Health Center between March 15 and April 14, 2020 (n=71)	DVT was seen in 37% of COVID-19 patients, predominantly in the male ones (67%, P=0.032). Patients with elevated D-dimer (mean of 5447 + 7032 ng/mL, P=0.0101) and alkaline phosphatase (110 UI, P=0.0095) correlated with a higher risk of DVT when suffering COVID-19.	There is a significant incidence of DVT in COVID-19 patients. Males are the ones with the highest risk for DVT. Elevated D-dimer and alkaline phosphatase are associated with a higher risk of DVT.
9	Marini C et al., 2022 [13]	United States of America	Retrospective cohort study at a level one trauma center comparing non-COVID-19 patients and those with the disease during March 20, 2019, and June 30, 2019 (n= 786, where 573 were non-COVID-19 patients and 213 were COVID-19 patients).	The incidence of DVT in COVID-19 patients was 33.8% whereas in non-COVID-19 patients that only 12.4% suffered from DVT. The elevation of D-dimer was associated with the incidence of DVT.	The incidence of DVT was higher in patients with COVID-19 than in those without it.
10	Thondapu V et al., 2021 [14]	United States of America	Retrospective cohort study on COVID-19 patients from March 13 to May 18, 2020 (n=138)	The incidence of venous thromboembolism in COVID-19 patients was 31.9% and specifically, of DVT, it was 20.2%. Patients with male sex, elevated C-reactive protein, and elevated platelet count at admission were the ones with the highest risk of venous thromboembolism in a COVID-19 context. Mortality in venous thromboembolism in COVID-19 patients increased in the presence of active malignancy, disseminated intravascular coagulation, and increased D-dimer.	COVID-19 is associated with DVT.
11	Li J et al., 2021 [15]	China	Retrospective cohort study of COVID-19 patients in 16 centers in China between January 1 to March 31, 2020 (n=2779)	Venous thromboembolism was seen in 5.94% of the severe hospitalized COVID-19 patients and in 2.79% of the non-severe ones. D-dimer had the highest association with DVT in COVID-19 patients.  However, DVT and COVID-19 patients also had higher levels of white blood cell count, neutrophils, and C-reactive protein and lower levels of fibrinogen. In 104 of their venous thromboembolism cases, 88 were of DVT.	DVT is prevalent in COVID-19 patients. Elevated D-dimer is a strong predictor of DVT in COVID-19 patients.
12	Avruscio G et al., 2020 [16]	Italy	Prospective cohort study of COVID-19 patients admitted to the Padua University Hospital from March 4 to April 30, 2020 (n= 85)	Venous thromboembolism was seen in 27.3% of COVID-19 patients in the medical ward and in 75.6% in the intensive care unit (p<0.0001). DVT happened in 42.4% of the patients. D-dimer has a strong association with venous thromboembolism in COVID-19 patients.	DVT has a significant incidence in COVID-19. D-dimer is strongly related to DVT in COVID-19.
13	Franco-Moreno A et al., 2020 [17]	Spain	Prospective study with COVID-19 patients with pulmonary embolism at the Infanta Leonor University Hospital from March 30, 2020, to May 6, 2020 (n=26)	The incidence of DVT in COVID-19 patients with pulmonary embolism was 7.7%.	DVT had a 7.7% incidence in COVID-19 patients who had suffered from pulmonary embolism.
14	Pancani R et al., 2020 [18]	Italy	Prospective study of admitted COVID-19 patients in three pulmonary units in Italy between March 27 and May 6, 2020 (n=68)	The incidence of DVT was observed in 3% of the COVID-19 patients	DVT has a low incidence in COVID-19 patients.
15	Brosnahan S et al., 2021 [19]	United States of America	Retrospective study of patients in the New York University Langone Health Manhattan Campus with thrombosis and with or without COVID-19 from March 1, 2020, to April 30, 2020 (n=129)	D-dimer, white blood cell count, C-reactive protein, ferritin, bilirubin, and transaminases were higher in patients with DVT and COVID-19. Of 40 patients with COVID-19, 19 of them suffered from above-the-knee DVT, which represents 47.5%.	The incidence of DVT increased after the COVID-19 pandemic.