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	Since this article does not have an abstract, we have provided the first 79 words of the full text and any section headings.

We read with interest the excellent review article on hypercoagulability syndromes by Thomas.¹ However, the author does not mention high altitude as an important predisposing factor for venous thrombosis. High altitude can precipitate thrombosis due to hypobaric hypoxia and its effect on the coagulation system—especially increased factor VIIa activity.^2-3 In addition, dehydration, polycythemia, and vascular spasms may also be involved in the increased tendency to venous thrombosis at high altitude.³

Ajit Singh Kashyap, MD; Surekha Kashyap, MD
Pune, India

1. Thomas RH. Hypercoagulability syndromes. Arch Intern Med. 2001;161:2433-2439. FREE FULL TEXT 2. Bendz B, Rostrup M, Sevre K, Andersen TO, Sandset PM. Association between acute hypobaric hypoxia and activation of coagulation in human beings. Lancet. 2000;356:1657-1658. FULL TEXT | ISI | PUBMED 3. Basnyat B, Graham L, Lee SD, Lim Y. A language barrier, abdominal pain, and double vision. Lancet. 2001;357:2022. PUBMED

Arch Intern Med. 2002;162:1783.