PubMed2001
Many acquired risk factors may be identified to avoid the scholarly nature of these interminable lists, they may be reclassified with respect to their originality or their mechanism of action and those of current interest, whose data is still often hypothetical but recent, can be underlined. The following order may be proposed: risk factors which cannot be changed: age (which remains the principal factor) and gender (women being at higher risk than men); true acquired risk factors such as cancer, dysimmune conditions (more specifically, the antiphospholipid syndrome) and hormone replacement therapy (oestroprogestative contraception which has been updated by the debate about "third generation pills" and the risk related to progesterone-like substances themselves; hormone replacement therapy of the menopause which still has no clinical trials to assess "our" forms with natural hormones administered transdermally or transmucosally). Smoking has also been accused of being a risk factor for venous thrombosis in the latest clinical trials. Metabolic factors increase the risk of thrombosis: this is established for obesity, still suspected for hyperhomocystonaemia, the abnormalities being the result of complex gene-environment interactions. Other dysmetabolic conditions (diabetes, hypercholesterolaemia, hypertriglyceridaemia), responsible for arterial complications, are not clearly related to increased venous thromboembolic risk although a preventive effect of statins (yet another I) has just been reported. Similarly to these metabolic factors, the origin of which, genetic or environmental, is difficult to establish, interest has recently been shown in quantitative and functional changes in blood clotting factors. This has been established for arterial disease for fibrinogen but, in addition to this factor which slightly increases the risk of venous thrombosis, increases of factor VIII independent of inflammatory conditions, of blood group and Von Willebrand factor, which all influence the level of factor VIII, an increase by 150% of the normal increases the risk of venous thromboembolic disease by 3 or 4 times. As for factor VIII, increases in factor IX, factor XI, and resistance to activated C protein (independently of the Leiden mutation on the gene for factor V), are also associated in increased venous thromboembolic risk. Without knowing into which category to classify them, previous personal and family history of thromboembolic disease, in the absence of the already mentioned hereditary risk factors, must be noted. Finally, amongst the acquired risk factors, the authors also list conditions of blood stasis and vascular lesions with or without hypercoagulability (surgery, prolonged hospital stays, cardiac failure, paralysis, pregnancy...). Of these acquired conditions which increase the risk of thrombotic complications, particular attention has been given over the last few years to forced immobilisation in uncomfortable positions as in certain forms of transport. Although clinical reports have discordant results, it would seem that the risk is increased and the benefits of supportive elastic stockings have been confirmed. If the acquired risk is identified and quantified for a patient, it allows evaluation of global risk and the installation of appropriate therapeutic measures.