title: Risk of venous thromboembolism after air travel: interaction with thrombophilia and oral contraceptives.
abstract: BACKGROUND
  Conflicting data are available on air travel as a risk factor for venous thromboembolism. To our knowledge, there are no studies investigating whether individuals with thrombophilia and those taking oral contraceptives are more likely to develop venous thromboembolism during flights than those without these risk factors.
  
  
  METHODS
  The study sample consisted of 210 patients with venous thromboembolism and 210 healthy controls. DNA analysis for mutations in factor V and prothrombin genes and plasma measurements of antithrombin, protein C, protein S, total homocysteine levels, and antiphsopholipid antibodies were performed.
  
  
  RESULTS
  In the month preceding thrombosis for patients, or the visit for controls, air travel was reported by 31 patients (15%) and 16 controls (8%), with an oddsratio of 2.1 (95% confidence interval, 1.1-4.0). Thrombophilia was present in 102 patients (49%) and 26 controls (12%), and oral contraceptives were used by 48 patients and 19 controls (61% and 27% of those of reproductive age, respectively). After stratification for the presence of air travel and thrombophilia, the odds ratio for thrombosis in individuals with both risk factors was 16.1 (95% confidence interval, 3.6-70.9). Stratification for the presence of air travel and oral contraceptive use gave an odds ratio of 13.9 (95% confidence interval, 1.7-117.5) in women with both risk factors.
  
  
  CONCLUSIONS
  Air travel is a mild risk factor for venous thromboembolism, doubling the risk of the disease. When thrombophilia or oral contraceptive use is present, the risk increases to 16-fold and 14-fold, respectively, indicating a multiplicative interaction.
authors.affiliation: Angelo Bianchi Bonomi Hemophilia and Thrombosis Center, Istituto di Ricovero e Cura a Carattere Scientifico, Maggiore Hospital, University of Milan, Milan, Italy.
authors.forename: Ida
authors.initials: I
authors.lastname: Martinelli
authors.forename: Emanuela
authors.initials: E
authors.lastname: Taioli
authors.forename: Tullia
authors.initials: T
authors.lastname: Battaglioli
authors.forename: Gian Marco
authors.initials: GM
authors.lastname: Podda
authors.forename: Serena Maria
authors.initials: SM
authors.lastname: Passamonti
authors.forename: Paola
authors.initials: P
authors.lastname: Pedotti
authors.forename: Pier Mannuccio
authors.initials: PM
authors.lastname: Mannucci
mesh_terms: D000328:Adult; D000368:Aged; D000401:Aircraft; D016022:Case-Control Studies; D003278:Contraceptives, Oral, Hormonal / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013577:Syndrome; D019851:Thrombophilia / Q000150:complications*; D014195:Travel; D020246:Venous Thrombosis / Q000453:epidemiology* / Q000209:etiology
chemical_list: D003278:Contraceptives, Oral, Hormonal