title: The BEST study--a prospective study to compare business class versus economy class air travel as a cause of thrombosis.
abstract: BACKGROUND
  As many as 10% of airline passengers travelling without prophylaxis for long distances may develop a venous thrombosis. There is, however, no evidence that economy class travellers are at increased risk of thrombosis.
  
  
  OBJECTIVE
  A suitably powered prospective study, based on the incidence of deep-vein thrombosis (DVT) reported in previous studies on long-haul flights, was designed to determine the incidence of positive venous duplex scans and D-dimer elevations in low and intermediate-risk passengers, comparing passengers travelling in business and economy class.
  
  
  METHODS
  Eight hundred and ninety-nine passengers were recruited (180 travelling business class and 719 travelling economy). D-dimers were measured before and after the flight. A value greater than 500 ng/ml was accepted as abnormal. A thrombophilia screen was conducted which included the factor V Leiden mutation, the prothombin 20210A mutation, protein C and S levels, antithrombin levels, and anticardiolipin antibodies immunoglobulin G (IgG) and immunoglobulin M (IgM). On arrival, lower limb compression ultrasonography of the deep veins was performed. Logistical regression analysis was used to determine the risk factors related to abnormally high D-dimer levels.
  
  
  RESULTS
  Only 434 subjects had a full venous duplex scan performed. None had ultrasonic evidence of venous thrombosis. Nine passengers tested at departure had elevated D-dimer levels and these volunteers were excluded from further study. Seventy-four of the 899 passengers had raised D-dimers on arrival. Twenty-two of 180 business class passengers (12%) developed elevated D-dimers compared with 52 of 719 economy class passengers (7%). There was no significant association between elevation of D-dimers and the class flown (odds ratio (OR) 0.61, p = 0.109). The factor V Leiden mutation, factor VIII levels and the use of aspirin were, however, associated with raised D-dimers (OR 3.36, p = 0.024; OR 1.01, p = 0.014; and OR 2.04, p = 0.038, respectively). Five hundred and five passengers were contacted within 6 months and none reported any symptoms of a clinical thrombosis or pulmonary embolus.
  
  
  CONCLUSIONS
  The incidence of ultrasonically proven DVT is much lower than previously reported. However, more than 10% of all passengers developed raised D-dimers, which were unrelated to the class flown. A rise in D-dimers is associated with an inherent risk of thrombosis and/or thrombophilia, demonstrates activation of both the coagulation and fibrinolytic systems during long-haul flights, and may indicate the development of small thrombi.
authors.affiliation: Departments of Haematology and Surgery, University of the Witwatersrand, and National Health Laboratory Service, Johannesburg.
authors.forename: Barry F
authors.initials: BF
authors.lastname: Jacobson
authors.forename: Marion
authors.initials: M
authors.lastname: Münster
authors.forename: Alberto
authors.initials: A
authors.lastname: Smith
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Burnand
authors.forename: Andrew
authors.initials: A
authors.lastname: Carter
authors.forename: A Talib O
authors.initials: AT
authors.lastname: Abdool-Carrim
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Marcos
authors.forename: Piet J
authors.initials: PJ
authors.lastname: Becker
authors.forename: Timothy
authors.initials: T
authors.lastname: Rogers
authors.forename: Dirk
authors.initials: D
authors.lastname: le Roux
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Calvert-Evers
authors.forename: Marietha J
authors.initials: MJ
authors.lastname: Nel
authors.forename: Robyn
authors.initials: R
authors.lastname: Brackin
authors.forename: Martin
authors.initials: M
authors.lastname: Veller
mesh_terms: D000328:Adult; D000401:Aircraft; D016022:Case-Control Studies; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis; D006801:Humans; D015994:Incidence; D007866:Leg / Q000098:blood supply; D008297:Male; D008875:Middle Aged; D018962:Phlebotomy; D011446:Prospective Studies; D012044:Regression Analysis; D013048:Specimen Handling; D014195:Travel; D014463:Ultrasonography; D020246:Venous Thrombosis / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000209:etiology*
chemical_list: D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D