Study suggests 1% risk of DVT for long-distance air travellers

December 18, 2003

Results of a study from New Zealand in this week's issue of THE LANCET suggest that the frequency of symptomatic venous thromboembolism (deep-vein thrombosis [DVT] or pulmonary embolism) could be around 1% for long-distance air travellers. This rate was found in a study of over 800 frequent long-haul air travellers identified as being at low to moderate risk-many of whom wore compression stockings or took aspirin as precautionary measures to prevent possible blood clots.

The true frequency of symptomless and symptomatic venous thromboembolism for long-haul air travellers is not known; a previous study (Lancet 2001; 357: 1485-89) suggested that symptomless DVT could occur in up to 10% of long-haul fliers. Richard Beasley from the Medical Research Institute of New Zealand and colleagues did a prospective study of long-haul air travelers to determine the frequency of symptomatic DVT and pulmonary embolism.

Volunteers were given a D-dimer blood test before flying; increases in D-dimer concentrations were used to identify individuals who may have developed thromboembolism. Overall, 878 people undertook long-haul flights (minimum duration four hours) over a six-week period. Those who became D-dimer positive or developed high clinical probability symptoms during the 3 months after travel were investigated with ultrasound and pulmonary angiography.

All participants travelled for at least 10 hours, with an average total duration of 39 hours travel over six weeks. 17% of travellers wore compression stockings and 31% took aspirin to reduce thrombosis risk. 112 patients with positive D-dimer results after flying were referred for radiological assessment. Frequency of venous thromboembolism associated with travel was 1% (9 out of 878), which included four cases of pulmonary embolism and five of deep venous thrombosis. Six patients with venous thromboembolism had pre-existing clinical risk factors, two had a recognised thrombophilic risk factor, two travelled exclusively in business class, five used aspirin, and four wore compression stockings.

Richard Beasley comments: "Our results suggest an association between multiple long distance air flights and venous thromboembolism, even in individuals at low to moderate risk. The role of traditional risk factors and prophylactic measures in air travel-related venous thromboembolism needs further investigation."

The study also shows that thrombosis may also occur for air travellers in Business Class as well as among those travelling in Economy Class. Professor Beasley adds: "The term 'Economy Class syndrome' is now redundant, with a better term being 'air-traveller's thrombosis'."
Lancet 2003; 362: 2039-44

Professor Richard Beasley,
Medical Research Institute of New Zealand,
PO Box 10055, 3rd Floor, 99 The Terrace,
Wellington, New Zealand;
T) 64-21-403060;
F) 64-4-472-9224;

NB: Professor Beasley will be available for media contact/interview on the telephone number above at the following times (all GMT):
Wednesday 17 December 1800-2100
Thursday 18 December 0600-0900 and 1800-2100
Friday 19 December 0600-0900


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