From the Guidelines
The diagnostic test of choice for Deep Vein Thrombosis (DVT) is a combination of pretest probability assessment, D-dimer testing, and compression ultrasound (CUS). This approach is favored due to its non-invasive nature, high accuracy, and ability to provide rapid results 1. The use of D-dimer testing as an initial screening tool is beneficial in ruling out DVT in patients with low clinical probability, but a positive result requires further testing with compression ultrasound 1.
Diagnostic Tests for DVT
- Compression Ultrasound (CUS): considered the first-line imaging test for DVT diagnosis
- D-dimer blood testing: used as an initial screening tool to measure protein fragments present when a blood clot is dissolving
- CT venography or MR venography: used in cases where ultrasound results are inconclusive or when pelvic or abdominal vein thrombosis is suspected
- Venography: historically the gold standard, but rarely used today due to its invasiveness and the availability of non-invasive alternatives
The combination of these diagnostic tests allows for accurate diagnosis and management of DVT, taking into account the patient's pretest probability and the results of each test 1. It is essential to note that the threshold for suspecting DVT and initiating diagnostic testing has lowered over the past few years, leading to a decrease in DVT prevalence in examined patients 1. As a result, the diagnostic standard for DVT should be adjusted accordingly, using Bayes' theorem to relate disease prevalence and failure rate 1.
From the Research
Diagnostic Tests for Deep Vein Thrombosis (DVT)
The diagnosis of DVT requires a multifaceted approach that includes clinical assessment, evaluation of pre-test probability, and objective diagnostic testing 2. The following are some of the diagnostic tests used for DVT:
- Clinical assessment: Common symptoms and signs of DVT are pain, swelling, erythema, and dilated veins in the affected limb 2.
- Pre-test probability assessment: The pre-test probability of DVT can be assessed using a clinical decision rule that stratifies DVT into "unlikely" or "likely" 2, 3.
- D-dimer test: If DVT is "unlikely", a D-dimer test can be used to rule out DVT. If the D-dimer level is normal, DVT can be excluded; if the D-dimer level is increased, further testing with compression ultrasound is recommended 2, 4, 5, 6.
- Compression ultrasound: If DVT is "likely" or if the D-dimer test is positive, compression ultrasound is used to confirm the diagnosis of DVT 2, 3, 6.
- Whole-leg compression ultrasound: This test can be used to diagnose DVT, especially in patients with a moderate pre-test probability and a negative D-dimer test 3.
Special Considerations
- Age-adjusted D-dimer: The D-dimer cut-off value can be adjusted based on the patient's age to improve the specificity of the test without compromising sensitivity 5.
- Wells rule: The Wells rule can be used to assess pre-test clinical probability, but it has a low diagnostic accuracy for isolated distal DVT 6.
- Isolated distal DVT: D-dimer has a better negative predictive value for isolated distal DVT, but alone it does not exclude isolated distal DVT 6.