From the Guidelines
To rule out deep vein thrombosis (DVT), a combination of clinical assessment, D-dimer testing, and imaging is typically used, with the Wells score being a validated tool for clinical probability assessment 1. When performing an examination to rule out DVT, the following steps should be taken:
- A clinical probability assessment should be performed using a validated tool like the Wells score, which evaluates risk factors such as active cancer, paralysis, recent immobilization, localized tenderness, entire leg swelling, calf swelling, pitting edema, collateral veins, and previous DVT 1.
- For patients with low clinical probability, a D-dimer blood test should be ordered; if negative, DVT can be safely excluded 1.
- However, if the D-dimer is positive or if the patient has moderate to high clinical probability, compression ultrasound of the affected leg should be performed, as it is the standard diagnostic tool with high sensitivity and specificity for proximal DVT 1.
- In cases where ultrasound results are inconclusive or if there is high clinical suspicion despite a negative initial ultrasound, a repeat ultrasound in 5-7 days may be necessary 1.
- For patients with suspected recurrent DVT, comparing with previous imaging is helpful 1. This systematic approach helps ensure accurate diagnosis while avoiding unnecessary testing for low-risk patients. It is also important to note that the treatment of choice for DVT is anticoagulation to reduce the risk of DVT extension, recurrent DVT, pulmonary embolism, and post-thrombotic syndrome, and that the benefits of anticoagulation therapy in patients with proximal DVT outweigh its risks 1.
From the Research
Examination to Rule Out Deep Vein Thrombosis (DVT)
To perform an examination to rule out DVT, the following steps can be taken:
- Clinical assessment: Evaluate the patient's symptoms and signs, such as pain, swelling, erythema, and dilated veins in the affected limb 2
- Pre-test probability: Assess the pre-test probability of DVT using a clinical decision rule, such as the Wells score or the primary care rule, to stratify DVT into "unlikely" or "likely" 3, 2
- D-dimer test: If DVT is "unlikely", refer for a D-dimer test. If the D-dimer level is normal, DVT can be excluded; if the D-dimer level is increased, refer for compression ultrasound 4, 2
- Compression ultrasound: If DVT is "likely" or if the D-dimer level is increased, refer for compression ultrasound to confirm the diagnosis 2, 5
- Limited-compression ultrasound: Limited-compression ultrasound can be used as a bedside test to rule out DVT, especially in patients with a low pre-test probability 5
Clinical Decision Rules
Clinical decision rules, such as the Wells score and the primary care rule, can be used to assess the pre-test probability of DVT. These rules take into account various clinical factors, such as:
- Calf swelling
- DVT as the most likely diagnosis
- Recent surgery or trauma
- Immobilization
- Cancer
- Pregnancy or postpartum state
- Family history of DVT 3, 6
D-dimer Test
The D-dimer test can be used to rule out DVT, especially in patients with a low pre-test probability. A negative D-dimer result can exclude DVT, while a positive result requires further testing with compression ultrasound 4, 2
- A study found that D-dimer as a stand-alone test had a failure rate of 1.8% (95% CI 0.8%-3.5%) for diagnosing DVT 4
- Another study found that the combination of D-dimer and clinical decision rules can safely exclude DVT in patients with a low pre-test probability 6
Compression Ultrasound
Compression ultrasound is the gold standard for diagnosing DVT. It can be used to confirm the diagnosis in patients with a high pre-test probability or in patients with a positive D-dimer result 2, 5
- A study found that limited-compression ultrasound had a sensitivity of 91% (95% CI 70% to 98%) and a specificity of 97% (95% CI 92% to 99%) for diagnosing DVT 5