The first step to diagnosis DVT is taking a detailed clinical history. This would include any risk factors for DVT, such as recent surgery, swelling after a long flight, recent trauma or a history of cancer. Family history is also important, as the patient may have a familial predisposition to abnormal clotting. Symptoms such as pain, pressure, aching and swelling of the leg should be reported.

A physical exam is the next step.

DVT can cause swelling, redness, and decreased mobility of the affected leg. The doctor will examine your calves and ankles, and check for edema and color changes.

The definitive test for DVT is an ultrasound of the deep veins of the legs, to check for the presence of a clot. This test should be done even in the absence of any symptoms, if there is any chance that a clot may be present.

The quality of the ultrasound is very important in order to assess the size, location, and age of the clot.

Ultrasound examinations are very operator dependent.

This means that vascular laboratories must be accredited to ensure they have qualified technicians performing the correct protocols.