OBJECTIVE TESTS are needed to confirm or exclude the diagnosis of venous thromboembolism because the accuracy of the clinical diagnosis is less than 50%.1,2 The most accurate tests available for the diagnosis of pulmonary embolism and deep venous thrombosis (DVT) are pulmonary angiography1 and contrast venographhy.3 With technically adequate studies, false-negative tests are rare. Therefore, a normal pulmonary angiogram is sufficient evidence to withhold treatment in patients with suspected pulmonary embolism,4 and a normal venogram precludes the need for therapy in patients with suspected DVT.5
Unfortunately, pulmonary angiography and venography are expensive, invasive tests that have associated morbidity, and are not available at all hospitals. Therefore, noninvasive tests play a critical role in the evaluation of patients with suspected venous thromboembolism.
Two noninvasive tests for deep venous thromboembolism, impedance plethysmography (IPG) and ultrasonography have an excellent correlation with venograms in patients with proximal DVT of