DVT of lower extremities is one of the most common cause for pulmonary embolism which in turn is responsible for majority of deaths. The duplex scan can diagnose many thrombi at a stage when no major changes have occurred in the venous haemodynamics and the patient is asymptomatic or minimally symptomatic.

It has been demonstrated that colour Doppler is as accurate as venography (proximalDVT–99.4%,distal DVT 93.1%) in the diagnosis of DVT , when used by experienced operators.