Evaluation of Deep Vein Thrombosis (DVT)
The optimal approach to evaluate a patient for DVT begins with clinical probability assessment using the Wells score, followed by appropriate diagnostic testing based on pretest probability, with D-dimer testing for low-probability patients and compression ultrasound for high-probability patients. 1, 2
Clinical Probability Assessment
The first step in evaluating a patient for DVT is to determine the pretest probability using the validated Wells score:
| 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/moderate pretest probability
Diagnostic Algorithm
For Low Pretest Probability Patients:
- Start with D-dimer testing (preferably a highly sensitive assay) 1, 2
- If D-dimer is negative → DVT excluded (no further testing needed)
- If D-dimer is positive → Proceed to compression ultrasound (CUS)
For High Pretest Probability Patients:
- Start with compression ultrasound (CUS) of proximal veins 1, 2
- If CUS is positive → Diagnose DVT and begin treatment
- If CUS is negative → Consider additional testing:
- D-dimer testing
- Serial ultrasound (repeat on day 7±1)
- Alternative imaging if high clinical suspicion persists
Special Considerations
For Suspected Upper Extremity DVT:
- Begin with combined modality ultrasound (compression with Doppler or color Doppler) 1
- If initial US is negative but clinical suspicion remains high:
- Perform D-dimer testing
- Consider serial ultrasound or venographic-based imaging (CT or MRI)
For Pregnant Patients:
- Start with compression ultrasound 1
- If negative, consider:
- Serial proximal CUS (day 3 and day 7)
- D-dimer testing (though less specific in pregnancy)
- For suspected isolated iliac vein thrombosis:
- Consider Doppler US of the iliac vein, MRI, or venography
For Suspected Recurrent DVT:
- Begin with proximal CUS or highly sensitive D-dimer 1
- If D-dimer is positive, proceed to proximal CUS
- A new non-compressible segment in common femoral or popliteal vein confirms recurrent DVT
When Initial Testing is Inconclusive
If initial testing is negative but clinical suspicion remains high:
- Consider serial ultrasound (repeat on day 7±1)
- Consider alternative imaging modalities:
Common Pitfalls to Avoid
- Relying solely on clinical examination - clinical assessment alone is unreliable with poor sensitivity and specificity 1, 3
- Missing isolated iliac vein thrombosis - standard proximal CUS may not visualize iliac veins adequately 2
- Overlooking distal DVT - ultrasound has lower sensitivity (63.5%) for below-knee DVT 2
- Delaying anticoagulation in high-risk patients - consider prophylactic anticoagulation while awaiting definitive diagnosis in high-risk patients 2
- Failing to consider alternative diagnoses - when DVT is ruled out, investigate other causes of symptoms 1
When to Initiate Treatment
- Confirmed DVT: Begin anticoagulation immediately 2
- High clinical suspicion awaiting confirmation: Consider prophylactic anticoagulation (e.g., enoxaparin 40 mg subcutaneously once daily) to balance thromboembolism risk against bleeding risk 2, 4
By following this structured approach to DVT evaluation, clinicians can efficiently and accurately diagnose or exclude DVT, ensuring appropriate treatment to reduce morbidity and mortality while avoiding unnecessary anticoagulation in patients without thrombosis.