A high pretest clinical probability and positive findings on noninvasive testing provide a definitive diagnosis of venous thrombosis. Patients with low pretest probabilities and positive findings on noninvasive testing and those with high pretest probabilities and negative findings on noninvasive testing should undergo venography. Of these, venography and venous ultrasonography are most widely used. Venography detects both proximal vein and calf vein thrombosis. For these reasons, this test has been replaced by IPG and venous ultrasonography for the diagnosis of most cases of suspected venous thrombosis.
Venous ultrasonography is the noninvasive method of choice for diagnosing venous thrombosis.
It is less painful and more convenient to perform than venography. The common femoral vein, superficial femoral vein, popliteal vein, and proximal deep calf veins are compressed with the transducer probe, and the results are observed on the monitor and reproduced in hard copies. Although venous ultrasonography fails to detect a substantial number of calf vein thrombi and small thrombi of the popliteal vein, this limitation is readily overcome. If the initial test result is normal, the test can be repeated in 7 days to detect the small number of thrombi that have extended since presentation. If the test remains negative after 7 days, the risk of thrombus extension to the proximal veins is negligible, and it is safe to withhold treatment.