What is the Wells criteria for Deep Vein Thrombosis (DVT)?

Wells Criteria for Deep Vein Thrombosis (DVT)

The Wells criteria is a validated clinical prediction rule that stratifies patients into probability categories for DVT and must be combined with D-dimer testing and/or ultrasound imaging for accurate diagnosis, not used alone. 1

Components of Wells Criteria

The Wells score consists of the following clinical features and point values:

• Active cancer (treatment ongoing, within 6 months, or palliative): +1 point
• Paralysis, paresis, or recent plaster immobilization of the lower extremities: +1 point
• Recently bedridden for >3 days or major surgery within 12 weeks: +1 point
• Localized tenderness along the distribution of the deep venous system: +1 point
• Entire leg swelling: +1 point
• Calf swelling >3 cm compared to asymptomatic leg: +1 point
• Pitting edema confined to the symptomatic leg: +1 point
• Collateral superficial veins (non-varicose): +1 point
• Previously documented DVT: +1 point
• Alternative diagnosis at least as likely as DVT: -2 points

Risk Stratification

Original Three-Tier Wells Score:

• Low probability: 0 or less points (≈5% prevalence of DVT)
• Moderate probability: 1-2 points (≈17% prevalence of DVT)
• High probability: 3 or more points (≈53% prevalence of DVT)

Modified Two-Tier Wells Score:

• DVT unlikely: 1 point or less (≈6% prevalence)
• DVT likely: 2 points or more (≈28% prevalence)

Diagnostic Algorithm Using Wells Criteria

1. Calculate the Wells score to stratify risk

2. For low probability/unlikely patients:

   • Perform highly sensitive D-dimer testing
   • If D-dimer negative: DVT excluded (safe to withhold treatment)
   • If D-dimer positive: Proceed to ultrasound imaging

3. For moderate/high/likely probability patients:

   • Proceed directly to proximal compression ultrasound (CUS) or whole-leg ultrasound
   • If positive: Treat for DVT
   • If negative proximal CUS: Consider serial ultrasound in 1 week or D-dimer testing

Important Clinical Considerations

• The Wells score performs better for predicting proximal DVT than isolated distal DVT 1, 2
• Performance is significantly reduced in hospitalized patients compared to outpatients 1, 3
• In inpatient settings, the Wells score performed only slightly better than chance with an area under the ROC curve of 0.60 3
• Performance is reduced in patients already receiving thromboprophylaxis 1
• Missed DVT can lead to pulmonary embolism with associated mortality rates of 25-30% 1

Limitations and Pitfalls

• Relying on Wells score alone is dangerous - it must be combined with D-dimer and/or imaging 4, 1
• D-dimer has limited utility in hospitalized patients, post-surgical patients, and pregnant women due to high frequency of positive results 1
• One-sixth of patients with distal DVT experience extension of thrombus proximally above the knee, requiring careful follow-up 4
• Individual clinical features alone have limited diagnostic value - the complete Wells score is more useful than any single component 5
• The "alternative diagnosis" component introduces subjectivity and may affect interobserver reliability 1

The Wells criteria remains a valuable tool for initial risk stratification of suspected DVT, but clinicians must understand its limitations and always incorporate it into a structured diagnostic pathway that includes objective testing.