Air Travel, Prothrombotic Mutations and Venous Thrombosis: The MEGA Study

Reviewer: Walter F. Sall, MD
The Abramson Cancer Center of the University of Pennsylvania
Last Modified: December 10, 2001

Presenter: Frits R. Rosendaal
Presenter's Affiliation: Leiden University Medical Center, Leiden, Netherlands
Type of Session: Scientific


  • Contradictory reports on air travel and deep venous thrombosis (DVT) risk have documented relative risk varying from 0 to 4.
  • Increasing public awareness of mortalities resulting from PE following extended airline flights makes further study of this issue warranted.
  • The Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis (MEGA) study is a case control study that currently has 829 cases and 829 controls enrolled. In this study, travel history with respect to DVT or PE risk was assessed

    Materials and Methods

  • Of the 829 enrolled cases, 465 had DVT while 341 had PE.
  • Cases were < 70 years of age. Controls were spouses or partners.
  • All patients were questioned about their travel history in the 3 months prior to their thrombotic event.
  • DNA samples were extracted for analysis of genetic risk factors including Factor V Leiden and prothrombin 20210A.


  • 30% of thrombotic events occurred within one week of travel.
  • RR of >4 hours of air travel was 6 compared to controls.
  • The presence of genetic risk factors alone led to a RR of 3. The combination of a genetic risk factor and airplane travel led to a 13-fold increase in RR.
  • The absolute risk of thrombotic event in a nine week follow-up period was 1:6000 for non-travelers without genetic risk factors, 1:1500 for plane travellers without risk factors and 1:500 for plane travellers with risk factors.

    Author's Conclusions

  • Recent plane travel does carry an increased relative risk of thrombosis for flights longer than 4 hours.
  • Genetic risk factors and plane travel appear to have a synergistic effect in causing DVT or PE.
  • Non-airplane travel greater than 4 hours carries only a 2-fold relative risk of thrombotic event.

    Clinical/Scientific Implications
    This case control study provides additional evidence supporting the role of immobility during airline travel as a risk factor for DVT/PE. Further study of behavioral modification (exercise), use of pressure stockings or seat size are needed to more precisely define who is at risk from airline flight. Currently a WHO Global Hazards of Travel study is underway which should shed more light on these issues.

    Oncolink's ASH Coverage made possible by an unrestricted Educational Grant from Amgen.

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