A case–control study of seated immobility at work as a risk factor for venous thromboembolism

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Abstract
Summary Objective: To determine the relative risk of prolonged seated immobility at work in patients with a deep vein thrombosis (DVT) or pulmonary embolism (PE). Design: A case–control study: cases and controls completed an interviewer-administered questionnaire to obtain information on risk factors for venous thromboembolism (VTE), including prolonged seated immobility at work. Univariate and multivariate logistic regression was used to determine the association between predicted variables and the probability of being a case or control. Participants: Cases were patients <65 years old attending the Wellington Hospital Outpatient VTE Clinic following hospital discharge for DVT and/or PE. Controls were patients <65 years old admitted to the Coronary Care Unit at Wellington Hospital. Setting: The Wellington Hospital Outpatient VTE Clinic and Coronary Care Unit. Main outcome measures: Odds ratio of VTE for prolonged seated immobility. Results: There were 97 cases (53 DVT, 29 PE, 15 DVT and PE), and 106 controls. In the multivariate analysis the odds ratio of VTE for prolonged seated immobility at work was 1.8 (95% CI 0.71–4.8). The maximum number of hours seated at work was associated with VTE, with the risk increasing by 10% per hour longer seated (odds ratio 1.1, 95% CI 1.0–1.2). The maximum number of hours seated at work without getting up was associated with VTE, with the risk increasing by 20% per hour longer seated (odds ratio 1.2, 95% CI 0.96–1.6). Conclusions: This study provides preliminary evidence that prolonged seated immobility at work may represent a risk factor for VTE.