Step 2 - Understanding your risks

Understanding your risks

When are you at risk of suffering from VTE?


After almost all surgical operations or procedures, there are certain changes in the blood and veins. The lining of the veins become more “sticky”, platelets (blood cells that cause clotting) increase in number, and blood flow slows. When combined with immobility – which may be part of recovering from surgery – these changes (also called “Virchow’s triad”) greatly increase the risk of VTE [1] .


Consequently, blood clots are much more likely to occur in the following circumstances:

  • Being in a hospital for any reason
    • Following any surgery, particularly surgery of the lower limb
    • Having your leg in plaster
    • After a major accident
  • Suffering from medical illnesses
    • History of blood clots (you or your family)
    • Cancer
    • Chronic illness including blood disorders
    • Suffering from varicose veins
    • Severe heart or lung disease
  • Personal risk factors
    • Increasing age – though young people can also get blood clots
    • Smoking
    • Being overweight
    • Using oral contraceptive pills or hormone replacement therapy
    • Being pregnant or having recently given birth.
  • Prolonged periods of sitting in a chair or bed rest
  • Travelling for long periods in an aircraft or motor vehicle


The level of risk of a blood clot forming after a procedure or operation varies, depending on the type of operation, the nature of the condition being treated and other risk factors (see above).


Hospitalised patients are at a 10-fold increased risk of VTE [2] (see Additional Resources on "Signs to watch for" page). In Australia and New Zealand, the annual incidence of deep vein thrombosis (DVT) among all hospitalised patients is around 160 per 100,000 [3] . For elective surgery patients, the Perioperative Mortality Review Committee (POMRC) of New Zealand indicates that here were approximately 8 pulmonary embolism-associated deaths per 100,000 admissions between 2006 and 2010 [4] .


[1] Frederick, A., & Frederick, S. (2003). Risk Factors for Venous Thromboembolism. Circulation, I9-I16.

[2] NZVTEP. (2012). National Policy Framework:VTE Prevention in Adult Hospitalised Patients in NZ. Wellington:HQSC

[3] Fletcher, J., MacLellan, D., Baker, R., Chong, B., Fisher, C., Flanagan, D., et al. (2007). Prevention of Venous Thromboembolism. The Australia and New Zealand Working Party on the Management and Prevention of Venous thromboembolism.

[4] POMRC. (2013). Perioperative Mortality in New Zealand: Second report of the Perioperative Mortality Review Committee. Wellington: Health Quality & Safety Commission.

*Southern Cross Hospitals Research Study. An exploration of patients’ engagement with and response to blood clot (venousthromboembolism; VTE) information and risk self-assessment tool provided to patients prior to surgery. Northern Y Ethics Committee approval NTY/12/01/004 (currently unpublished).