From the Guidelines
Yes, there is a point to ordering both a venous ultrasound of the lower extremity and a D-dimer test in a patient with suspected deep vein thrombosis (DVT), even before either test is resulted, as this approach allows for comprehensive evaluation and can expedite diagnosis and treatment. The D-dimer is a sensitive screening test that, when negative, can effectively rule out DVT in low-risk patients, while the ultrasound provides direct visualization of clots and is considered the gold standard diagnostic test 1. By ordering both simultaneously, you avoid delays in diagnosis that would occur if tests were ordered sequentially. If the D-dimer returns positive but the ultrasound is negative, you still have valuable information to guide further management, as a positive D-dimer may indicate the need for additional imaging or repeat ultrasound in certain cases.
According to the American Society of Hematology 2018 guidelines, a highly sensitive D-dimer assay is required for diagnosis, and a negative D-dimer rules out DVT, with no additional testing or anticoagulation required 1. However, the guidelines also recommend against using a positive D-dimer alone to diagnose DVT and against additional testing following negative proximal or whole-leg ultrasound in a population with low prevalence/pretest probability (≤10%) 1.
Key considerations in testing decisions include:
- Clinical judgment guiding testing decisions
- Patient's pretest probability of DVT
- Risk factors
- Clinical presentation
- The use of highly sensitive D-dimer assays
- The role of ultrasound in providing direct visualization of clots
In patients with suspected DVT, the approach to diagnosis should be guided by the patient's pretest probability, with simultaneous ordering of D-dimer and ultrasound being a reasonable approach to expedite diagnosis and treatment, particularly in emergency settings 1.
From the Research
Diagnostic Approach
The diagnostic approach for suspected deep vein thrombosis (DVT) or pulmonary embolism (PE) typically involves a combination of clinical evaluation, D-dimer testing, and imaging studies such as venous ultrasonography or computed tomography (CT) scans 2, 3, 4, 5.
Role of D-dimer Testing
D-dimer testing is a useful screening tool for DVT and PE, with high sensitivity but low specificity 3, 6, 5. A negative D-dimer result can help rule out DVT or PE, especially when combined with a low clinical probability score 5. However, a positive D-dimer result may not necessarily confirm the diagnosis due to its low specificity.
Role of Venous Ultrasonography
Venous ultrasonography, particularly compression ultrasonography (CUS), is a valuable diagnostic tool for DVT, with high sensitivity and specificity for detecting proximal DVT 3, 4, 5. A single negative CUS result can safely exclude DVT in patients with a low clinical probability score, but repeated testing may be necessary in some cases 5.
Sequential Testing Approach
A sequential testing approach, combining clinical evaluation, D-dimer testing, and venous ultrasonography, can safely and efficiently diagnose or exclude DVT and PE 2, 6, 5. This approach can reduce the need for unnecessary imaging tests and anticoagulant treatment.
Key Findings
- A negative D-dimer result and a low clinical probability score can safely exclude DVT or PE 5.
- A single negative CUS result can safely exclude DVT in patients with a low clinical probability score 5.
- Repeated CUS testing may be necessary in some cases to exclude DVT 5.
- The combination of clinical assessment, D-dimer testing, and CUS can reduce the need for helical spiral CT by 40% to 50% 5.
Ordering a Venous Ultrasound and D-dimer Test
Based on the available evidence, ordering a venous ultrasound and D-dimer test before the results are available may not be necessary in all cases. A sequential testing approach, combining clinical evaluation, D-dimer testing, and venous ultrasonography, can safely and efficiently diagnose or exclude DVT and PE 2, 6, 5. However, the decision to order these tests should be based on individual patient factors, such as clinical presentation and risk factors, and should be guided by a validated clinical decision rule 2, 4.