What is considered the best initial diagnostic study for deep vein thrombosis (DVT)?

Venous duplex ultrasound is considered the best initial diagnostic study for deep vein thrombosis (DVT) due to its high sensitivity and specificity for detecting thrombi in the deep veins of the legs. This non-invasive imaging technique uses sound waves to create images of the blood flow and helps in visualizing the venous structures directly.

The ultrasound can identify the presence of a thrombus by detecting changes in the normal flow of blood or by visualizing the thrombus itself. It is widely available in healthcare settings and can be performed quickly and safely, making it the first-line investigation in suspected cases of DVT.

While the D dimer test is useful as a screening tool to rule out DVT, it is not specific and can be elevated in various conditions, including recent surgery, infections, and malignancy. CT venography and radiographic contrast venography are more invasive and are typically reserved for cases where ultrasound results are inconclusive or if there's a need to visualize the pelvic veins or other areas not adequately assessed by duplex ultrasound. These methods involve the use of contrast agents and entail a higher risk of complications, making them less favorable as initial diagnostic options.