Wells Score for DVT
The Wells score for DVT stratifies patients into low, moderate, and high pretest probability groups to guide D-dimer and imaging decisions in suspected deep vein thrombosis.
inputs
✓ when to use
Use in ambulatory adult patients presenting with signs or symptoms suggesting DVT (unilateral leg swelling, pain, warmth). The score determines the appropriate diagnostic pathway: low probability → D-dimer → if negative, exclude DVT; high probability → proceed directly to ultrasound.
✗ when not to use
Not validated in hospitalised patients (who have high baseline DVT risk), pregnant patients, patients already on anticoagulation, or those with suspected upper extremity DVT. The 'alternative diagnosis' criterion is subjective. In patients with prior DVT in the same leg, ultrasound interpretation may be complicated by residual vein changes.
clinical pearls
- The 'alternative diagnosis as likely' criterion (-2 points) is the most impactful single item and the most subjective. Document your reasoning when you apply or don't apply this deduction.
- In the two-level Wells model (used in some UK pathways), ≤1 = 'DVT unlikely' and ≥2 = 'DVT likely'. This binary version is simpler and performs comparably to the three-level model.
- D-dimer is only useful for RULING OUT DVT in low-to-moderate probability patients. In high probability patients, a negative D-dimer does not exclude DVT — proceed to ultrasound regardless.
- If the initial ultrasound is negative but clinical suspicion remains (moderate/high probability with negative scan), repeat ultrasound in 5–7 days. Isolated calf DVT can be missed on initial scanning.
- Measure calf circumference at a standardised point — 10 cm below the tibial tuberosity. A >3 cm difference between legs is the criterion, not absolute calf size.