From the Guidelines
Venous duplex ultrasound is the preferred initial imaging test to rule out deep vein thrombosis (DVT) due to its high sensitivity and specificity for proximal DVT, as reported in a recent study 1. This non-invasive imaging test combines traditional ultrasound with Doppler flow assessment to visualize blood clots and evaluate blood flow in the veins. The test typically takes 30-45 minutes and involves applying gel to the skin while a technician moves a transducer over the area of concern. No special preparation is needed, and results are usually available quickly. Some key points to consider when using venous duplex ultrasound to rule out DVT include:
- High sensitivity (95%) and specificity (96%) for proximal DVT in symptomatic patients, making it highly reliable 1
- Less consistent in diagnostic performance above the inguinal canal and below the knee, as noted in a study published in the Journal of the American College of Radiology 1
- If the venous duplex is negative but clinical suspicion remains high, additional testing such as D-dimer blood tests or repeat ultrasound in 5-7 days may be warranted, as suggested by the American Society of Hematology 2018 guidelines for management of venous thromboembolism 1
- The reliability of venous duplex stems from its ability to directly visualize thrombi and assess blood flow dynamics, rather than relying on indirect markers of thrombosis. It is also important to note that other imaging modalities, such as contrast-enhanced CT venography (CTV) and magnetic resonance venogram (MRV), may be used in certain cases, particularly when ultrasound results are negative or indeterminate, as recommended by the National Comprehensive Cancer Network 1.
From the Research
Venous Duplex and DVT Diagnosis
- Venous duplex ultrasonography is a commonly used diagnostic tool for deep vein thrombosis (DVT) 2, 3.
- The combination of a negative Wells score and negative plasma D-dimer level can safely exclude the presence of DVT, making venous duplex scanning unnecessary for these patients 4.
- However, patients with a positive D-dimer level and positive Wells score will benefit from whole leg venous duplex scanning to rule out the presence of high-risk DVT 4.
Accuracy of Venous Duplex
- Venous duplex scanning has been shown to have a high sensitivity and specificity for diagnosing femoropopliteal DVT, with a specificity of 100% and a sensitivity of 95% in one study 2.
- However, the accuracy of venous duplex scanning may be lower for calf DVT, with nearly all errors arising in the diagnosis of calf DVT in one study 2.
Indications for Venous Duplex Scanning
- The presence of sudden onset of unilateral swelling is a strong predictor of acute DVT, and venous duplex scanning is likely warranted in these cases 3.
- Mild unilateral symptoms with a coexistent risk factor may also warrant venous duplex scanning, as the prevalence of acute DVT is around 10-20% in these cases 3.
- However, chronic unilateral swelling or bilateral swelling without risk factors is less likely to be associated with acute DVT, and venous duplex scanning may not be necessary in these cases 3.
D-Dimer Levels and Venous Duplex Scanning
- Different D-dimer levels can be used to reduce the need for venous duplex scanning in patients with symptomatic pulmonary embolism, particularly in those with low and moderate pretest clinical probability 5.
- A combination of specific D-dimer level and clinical probability score can be effective in excluding DVT in low pretest probability patients 5.