Compression sonography for the exclusion of deep vein thrombosis: can I trust my eyes?

In spite of great advances in the diagnosis and treatment of venous thromboembolic disease achieved in the last decade, the diagnosis of lower-limb deep vein thrombosis (DVT) still remains a daily challenge to health-care professionals all around the world. Clinical diagnosis alone is not reliable (only in approximately one third of patients with suspected DVT the diagnosis is confirmed by objective testing) (1), the spontaneous course of the disease is unfavourable (mortality due to pulmonary embolism in untreated patients exceeds 20%) (1), and methods of treatment are effective but potentially harmful (approximately 4.5% major bleeding events under anticoagulation) (2). Thus, additional tests are required for establishing or ruling out the diagnosis. Traditionally, venography has been the method of choice for the evaluation of patients with suspected deep vein thrombosis, but because of its invasiveness,relatively high costs, technical demands, and the risks associated with contrast dye it is far from being ideal. In recent years it has been widely replaced by compression ultrasound (CUS) (3), which is an excellent noninvasive, relatively cheap test for the diagnosis of proximal deep vein thrombosis (with sensitivity and specificity both above 97%), but has a markedly lower sensitivity for the detection of distal (calf) vein thrombosis (1, 2, 4). Calf vein thrombosis very seldom causes lethal pulmonary embolism but may propagate to the proximal veins in about 25% of cases (5, 6). Therefore, two negative CUS limited to the proximal leg veins (including the popliteal vein) obtained seven days apart are usually required for the exclusion of deep vein thrombosis (so called “serial CUS-testing”) (3, 4). In recent years the wide availability of CUS as a rapid and non-invasive tool for diagnosis or exclusion of DVT led to an increasing number of ultrasound studies in patients with low clinical probability of DVT. Do we have to refer them all to serial CUS-testing? Most of the guidelines and statements on the diagnosis of DVT published recently rely on alternative strategies, combining CUS limited to the proximal veins of the legs (including the popliteal vein) with the assessment of clinical pre-test probability and/or the performance of D-dimer testing (which both have been shown to enhance the predictive value of a negative CUS) (1, 7, 8) and serial CUS-testing or venography performed only in patients with intermediate or high clinical risk or a positive D-dimer test. These approaches have been shown to be safe and more cost-effective in the exclusion of deep vein thrombosis than serial CUS (7-10). In this issue of Thrombosis and Haemostasis two prospective studies dealing with exclusion of deep vein thrombosis by a single CUS of the whole leg (including the calf veins) are published (11, 12). The failure rate of this strategy turned out to be low: in the study by Elias et al. 0.5% and in the study by Schellong et al. 0.3% of patients tested negative for DVT developed venous thromboembolic events during a 3-month followup, which is at least as good as the three-month-failure rate reported with other strategies including the combination of clinical risk assessment and serial CUS, D-dimer testing and serial CUS, or even single venography with high-osmolar contrast dye (7, 9, 13-16). Both studies have several points in common: Both groups mainly relied on the least expensive method of ultrasound, B-mode sonography, and restricted the use of colour-coded Doppler for the assessment of respiratory flow modulation in the common femoral vein to exclude isolated thrombosis of the iliac veins. Both groups used high-quality ultrasound equipment (which might especially be important for the assessment of the relatively small calf veins). All ultrasound studies were performed by well trained operators (which is generally important for ultrasound studies). All CUS-studies were performed Compression sonography for the exclusion of deep vein thrombosis: can I trust my eyes?