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Three studies of venous thrombosis after long-haul flights give risk estimates

Long-haul flights of 8 hours and longer double the risk for isolated calf muscle venous thrombosis

In the December 8 issue of Annals of Internal Medicine there are three articles on thromboembolism after long-haul flights. In the first German researchers assessed the incidence of venous thrombosis associated with long-haul flights in a prospective, controlled cohort study of 964 passengers returning from long-haul flights (flight duration, 8 hours or more) and 1213 non-traveling control subjects.

They diagnosed venous thrombotic events in 27 passengers (2.8%) and 12 controls (1.0%) (risk ratio [RR], 2.83). Of these, 20 passengers (2.1%) and 10 controls (0.8%) presented with isolated calf muscle venous thrombosis (RR, 2.52), whereas 7 passengers (0.7%) and 2 controls (0.2%) presented with deep venous thrombosis (RR, 4.40). Symptomatic pulmonary embolism was diagnosed in 1 passenger with deep venous thrombosis (P = 0.44). All of these individuals had normal findings at baseline ultrasonography. Passengers with isolated calf muscle venous thrombosis or deep venous thrombosis had at least 1 risk factor for venous thrombosis (>45 years of age or elevated body mass index in 21 of 27 passengers). The follow-up after 4 weeks revealed no further venous thromboembolic event.

These researchers concluded: "Long-haul flights of 8 hours and longer double the risk for isolated calf muscle venous thrombosis. This translates into an increased risk for deep venous thrombosis as well. In our study, flight-associated thrombosis occurred exclusively in passengers with well-established risk factors for venous thrombosis.

Arch Intern Med. 2003;163:2759-2764. December 8, 2003 © 2003 American Medical Association. All rights reserved. ICPC-2 Category K. Circulatory
Venous Thrombosis After Long-haul Flights, Thomas Schwarz, MD; Gabriele Siegert, MD; Wolfram Oettler, MD; Kai Halbritter, MD; Jan Beyer, MD; Roswitha Frommhold, RN; Siegmund Gehrisch, MD; Florian Lenz, BS; Eberhard Kuhlisch, PhD; Hans-Egbert Schroeder, MD; Sebastian M. Schellong, MD

Air travel is a risk factor for pulmonary thromboembolism; the incidence increases with the duration of the air travel

In the second study, Spanish researchers assessed the incidence of symptomatic pulmonary thromboembolism (PTE) in passengers on long-haul flights arriving at Madrid Airport between 1995 and 2000, and the association with the number of flight hours.

They found that the average number of passengers per year who arrived at the airport on flights originating abroad in the period analyzed was 6 839 222. 16 cases of PTE were detected over the 6-year period. All patients with travel-associated PTE had flight durations of greater than 6 hours. The overall incidence of PTE was 0.39 per 1 million passengers. On flights that lasted between 6 and 8 hours, the incidence was 0.25 per 1 million passengers, while on flights longer than 8 hours, the incidence was 1.65 per 1 million passengers (P<.001).

The researchers concluded: "Air travel is a risk factor for PTE, and the incidence of PTE increases with the duration of the air travel. However, the low incidence of PTE among long-distance passengers, similar to that observed in other international airports, does not justify social alarm."

Arch Intern Med. 2003;163:2766-2770. December 8, 2003 © 2003 American Medical Association. All rights reserved.
Incidence of Air Travel-Related Pulmonary Embolism at the Madrid-Barajas Airport, Esteban Pérez-Rodríguez, MD; David Jiménez, MD; Gema Díaz, MD; Ivan Pérez-Walton, MD; Manuel Luque, MD; Carmen Guillén, MD; Eva Mañas, MD; Roger D. Yusen, MD

When thrombophilia or oral contraceptive use is present, the risk of venous thromboembolism after long-haul flights increases to 16-fold and 14-fold

In the third study, Italian researchers investigated whether individuals with thrombophilia and those taking oral contraceptives are more likely to develop venous thromboembolism during flights than those without these risk factors. The study sample consisted of 210 patients with venous thromboembolism and 210 healthy controls. DNA analysis for mutations in factor V and prothrombin genes and plasma measurements of antithrombin, protein C, protein S, total homocysteine levels, and antiphsopholipid antibodies were performed.

They found that in the month preceding thrombosis for patients, or the visit for controls, air travel was reported by 31 patients (15%) and 16 controls (8%), with an odds ratio of 2.1. Thrombophilia was present in 102 patients (49%) and 26 controls (12%), and oral contraceptives were used by 48 patients and 19 controls (61% and 27% of those of reproductive age, respectively). After stratification for the presence of air travel and thrombophilia, the odds ratio for thrombosis in individuals with both risk factors was 16.1. Stratification for the presence of air travel and oral contraceptive use gave an odds ratio of 13.9 in women with both risk factors.

The researchers concluded: "Air travel is a mild risk factor for venous thromboembolism, doubling the risk of the disease. When thrombophilia or oral contraceptive use is present, the risk increases to 16-fold and 14-fold, respectively, indicating a multiplicative interaction."

Arch Intern Med. 2003;163:2771-2774. December 8, 2003 © 2003 American Medical Association. All rights reserved.
Risk of Venous Thromboembolism After Air Travel - Interaction With Thrombophilia and Oral Contraceptives, Ida Martinelli, MD, PhD; Emanuela Taioli, MD, PhD; Tullia Battaglioli, MD; Gian Marco Podda, MD; Serena Maria Passamonti, MD; Paola Pedotti, BSc; Pier Mannuccio Mannucci, MD
Posted on Global Family Doctor 16 December 2003