Successful and cost-effective prophylaxis against venous thromboembolism (V
TE) depends on the availability of safe and effective antithrombotic method
s, and the ability to match these to patients according to their level of t
hromboembolic risk. The last 20 years have seen significant developments in
methods of thromboprophylaxis but, despite use of the best available metho
ds, VTE still occurs in a significant proportion of patients. Efforts are n
ow focused both on developing more effective pharmacological and physical m
ethods, and improving assessment of thromboembolic risk in clinical practic
e, with the goal of avoiding unnecessary prophylaxis in low-risk patients a
nd providing enhanced protection to high-risk patients. Factors known to ex
ert a direct effect on thromboembolic risk include previous VTE, advancing
age, surgery, malignancy, immobility, and the presence of thrombophilic sta
tes. Other less well-defined risk factors include obesity, pregnancy and le
g varicosities. Various risk assessment models (RAMs) have been devised bas
ed on these factors, but most of the resulting risk assessment formulae, so
me of them based on laboratory test results, have been too complicated to g
ain acceptance in routine clinical practice. Reflecting the need to refine
the use of thromboprophylaxis in clinical practice, a number of RAMs have b
een developed recently, based on epidemiological evidence. Some models incl
ude specific recommendations for prophylaxis, based on evidence from random
ized, controlled trials, (C) Lippincott Williams & Wilkins.