Ruling Out Deep Vein Thrombosis (DVT)
The optimal strategy to rule out DVT is to first assess pretest probability using the Wells score, then perform either D-dimer testing (for low/moderate probability) or compression ultrasound (for high probability), with appropriate follow-up testing based on initial results. 1
Step 1: Assess Pretest Probability Using Wells Score
Calculate the Wells score to stratify patients into probability categories:
| Factor | Points |
|---|---|
| Active cancer | 1 |
| Paralysis, paresis, or recent immobilization | 1 |
| Bedridden ≥3 days or major surgery within 12 weeks | 1 |
| Localized tenderness along deep veins | 1 |
| Entire leg swollen | 1 |
| Calf swelling ≥3 cm larger than asymptomatic side | 1 |
| Pitting edema confined to symptomatic leg | 1 |
| Collateral superficial veins | 1 |
| Previous DVT | 1 |
| Alternative diagnosis at least as likely | -2 |
- Score ≥2: High pretest probability
- Score <2: Low pretest probability
Step 2: Initial Testing Based on Pretest Probability
For Low/Moderate Pretest Probability:
- Order a highly sensitive D-dimer test 2, 1
- If D-dimer is negative: DVT is ruled out, no further testing needed
- If D-dimer is positive: Proceed to compression ultrasound
For High Pretest Probability:
- Order proximal compression ultrasound (CUS) or whole-leg ultrasound 2, 1
- D-dimer testing alone is not recommended in high probability patients 2
Step 3: Follow-up Testing
If initial proximal CUS is negative but high clinical suspicion remains:
- Perform one of the following 2, 1:
- Repeat proximal CUS in 1 week
- Whole-leg ultrasound
- Highly sensitive D-dimer (if not already done)
If extensive unexplained leg swelling with negative ultrasound:
If ultrasound is impractical or nondiagnostic:
- Consider CT venography, MR venography, or MR direct thrombus imaging 2
Special Considerations
Comorbid conditions with elevated D-dimer: For patients with cancer, inflammation, pregnancy, recent surgery, or advanced age, initial testing with ultrasound is preferred over D-dimer 2, 1
Recurrent DVT: For suspected recurrent DVT, initial evaluation with proximal CUS or highly sensitive D-dimer is recommended over venography 2
Upper extremity DVT: Initial evaluation with combined modality ultrasound (compression with either Doppler or color Doppler) is suggested 2
Pregnancy: Compression ultrasound with serial evaluations (days 0,3, and 7) if initial test is negative 1
Ultrasound Technique
Complete duplex ultrasound should include 2, 1:
- Compression of deep veins from inguinal ligament to ankle
- Assessment of posterior tibial and peroneal veins in calf
- Spectral Doppler waveforms and color Doppler images
The major diagnostic criterion is failure of complete compression of vein walls when pressure is applied during real-time imaging 2.
Common Pitfalls to Avoid
- Relying solely on clinical symptoms for diagnosis 1, 3
- Not assessing pretest probability before ordering tests 1
- Using D-dimer as a stand-alone test in high probability patients 2
- Failing to image iliac veins in patients with extensive unexplained swelling 2, 1
- Not performing follow-up testing when initial tests are negative but clinical suspicion remains high 2, 1
- Overlooking non-vascular causes of leg swelling (lymphedema, lipedema, cardiac failure) 1
By following this evidence-based approach, clinicians can effectively rule out DVT while minimizing unnecessary testing and treatment, ultimately improving patient outcomes related to morbidity, mortality, and quality of life.