JHScurr et al Lancet. May (2001) Vol. 357 #9267 p 1485.
A study of the development of deep vein thrombosis during long distance flights (>8hours).
89 males and 142 females aged over 50 with no recorded history of thromboembolism volunteered in response to an advert. All were scheduled to undertake a journey involving continuous flight for more than 8 hours.
30 of them were used as controls by making measurements 2 weeks and then 2 days before travel. In this way the potential for development of signs of DVT in absence of air travel could be tentatively assessed.
Those volunteers that were retained in the study (231 out of 479) after selection (rejects were either medical or logistic) were randomly assigned to use a lower leg elasticized stocking or, no stocking.
The presence of early signs of thromboembolism were determined by ultrasonography of the calf muscles and D dimer assay (from blood samples) before and after travel.
10% (95% CI = 4.8,16.0) developed symptomless DVT in the calf, if no stocking was worn during travel.
The stocking wearing group had no DVT 0% (95% CI = 0.0, 3.1).
Symptomless calf DVT is not a major risk to health. The study shows that early signs of a risk of DVT can be detected in a reasonably practicable manner for the purposes of research.
It can be anticipated that other studies of potential methods to prevent DVT will be based on the methodology reported here.
However, such studies would be more convincing if there were a larger control group and if measurements were repeated for a longer period prior to and after travel. It may be that the study size was too small for there to have been a chance of including a case of new DVT.
This work has not shown that the use of elasticized stockings prevents serious DVT, it shows only that their use may reduce a risk of signs of early DVT. Other work shows that early signs of DVT in this age group may be quite common.