Table 4.

Characteristics of retrospective COVID-19 studies on venous thromboembolism incidence rate and predictors

Study	Country	Study type, time period	Total number of cases	Venous thromboembolism incidence rate	Analysis performed	Identified predictors
Cohen et al.	United States	Retrospective, March 1st to April 27th, 2020	9407	2.9% (2.4% in medical ward and 4.9% in ICU)	Multivariate analysis	For VTE or mortality: 1.Advanced age 2.Increasing Charlson Comorbidity Index 3.History of cardiovascular disease 4.ICU level of care, and 5.Elevated maximum D-dimer with a cutoff at least four times the upper limit of normal
Dalager- Pedersen et al.	Denmark	Retrospective, January 27th to June 1st, 2020	1540	5% VTE (both ICU and general ward)	30-day absolute risks	This Study compared COVID-19 and non-COVID-19 patients showed COVID-19 patients had a higher risk of VTE
Freund et al.	France, Spain, Belgium, Italy, Chile, Canada	Retrospective, February 1st to April 10th, 2020	974	15% (only PE, DVT not studied)	Multivariable binary logistic regression	1. Male gender 2. Age > 48 3. Heart rate 4. Prior history of VTEs 5. Clinical signs of DVT 6. Recent immobilization
Mei et al.	China	Retrospective, January 1st to March 23rd, 2020	616	2% VTE (DVT and/or PE)	χ2 test, Fisher exact test, t test, and Mann–Whitney U test	This study compared Padua score in COVID-19 pneumonia and community-acquired pneumonia
Poissy et al.	France	Retrospective case series, February 27th to March 31st, 2020	196 (ICU patients only)	6.1% (PE only)	Simple descriptive analysis	None
Rieder et al.	China	Retrospective, March 26th to April 20th, 2020	49	6.1%	Spearman test	The level of D-dimers at hospital admission and the maximum level during follow-up were correlated with days at the hospital, days in ICU, days on non-invasive ventilation, or days on invasive ventilation

DVT deep vein thrombosis, ICU intensive care unit, PE pulmonary embolism, VTE venous thromboembolism