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
Background 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.
Results 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.
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.
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