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LINK BETWEEN DEEP-VEIN THROMBOSIS AND LONG-HAUL AIR TRAVEL STILL IN DOUBT (pp 1461, 1485)

May 09, 2001

Results of the first prospective randomised controlled trial to assess the effects of long-haul air travel and the risk of symptomless deep-vein thrombosis (DVT) are detailed in this week's issue of THE LANCET. Authors of an accompanying Commentary article conclude that the study does not resolve the long-standing controversy of the assumed association between DVT and air travel, and state that more research in this area is required.

The frequency of clinically important DVT during long-haul air travel is unknown. New research into so-called 'economy-class syndrome', by John Scurr and colleagues from University College London, UK, has been the subject of considerable media speculation over the past six months. The study found that of 200 passengers taking a long-haul air flight (minimum duration 8 hours), passengers who wore special compression stockings throughout the flight had no evidence of symptomless DVT assessed by ultrasonography within 48 hours of flying; however, 10% of passengers in the group not given stockings were found to have symptomless DVT in their calf veins. How many of those with symptomless DVT would go on to develop symptomatic DVT is not known.

An accompanying Commentary article (p 1461) by Jack Hirsh and Martin O'Donnell from McMaster University, Ontario, Canada assesses Scurr and colleagues' study, taking into account previous research into long-haul travel and risk of DVT. They state that there are two main reasons why Scurr and colleagues' study does not resolve the issue of long-haul air travel and the risk of DVT. They comment that the reported incidence of symptomless thrombosis among the controls was at least 40-fold higher than previous estimates, and propose that this unexpected high rate might have been attributed to inadvertent biased ultrasonographic assessment. They add that the fact that the diagnosis of calf-vein thrombosis was associated with a negative D-dimer (a very sensitive test for venous thrombosis) suggests that the thrombi were either very small or were false-positive findings. They also note that none of the positive ultrasonographic tests in Scurr and colleagues' study were followed-up for confirmation by venography.

Jack Hirsh comments: "If the results of the randomised trial are valid, they should be easy to reproduce, and if confirmed they would clearly establish lengthy air travel as an important risk factor for thrombosis". He adds: "What is needed are rigorously designed and adequately powered studies to resolve the problem, as agreed at a meeting of scientists and the airline industry organised by the WHO on March 12-13. Until more definitive information becomes available, however, it is reasonable to continue to recommend simple measures for long-distance travellers, such as regular isometric muscle contraction and adequate hydrationIt would be premature to legislate that airlines change the seating configuration or introduce other costly prophylactic procedures until there is more information on the extent of the problem and on the effectiveness of much simpler preventive measures".

Contact: Mr J H Scurr, Lister Hospital, Chelsea Bridge Road, LONDON SW1W 8RH, UK; T) +44 (0)20 7259 9216; F) +44 (0)20 7259 9221; E) Jscurr@uk-consultants.co.uk

Dr Jack Hirsh, Hamilton Civic Hospitals Research Centre, McMaster University, Hamilton, Ontario L8V 1C3, Canada; T) +1 905 527 2299; x 2601; F) +1 905 575 2646; E) jhirsh@thrombosis.hhscr.org)

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