What are the Wells criteria for assessing deep vein thrombosis (DVT)?

Wells Criteria for Deep Vein Thrombosis (DVT)

The Wells criteria is a validated clinical prediction tool that stratifies patients into risk categories for DVT, allowing clinicians to determine the need for additional diagnostic testing. 1

The Wells Score Components

The Wells score for DVT includes the following clinical features:

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

Risk Stratification

The Wells score can be interpreted using either the three-tier or two-tier system:

Three-Tier System:

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

Two-Tier System (Modified Wells):

• DVT unlikely: Score of 1 or less (6% prevalence of DVT)
• DVT likely: Score of 2 or more (28% prevalence of DVT)

Clinical Application Algorithm

1. Calculate Wells score for all patients with suspected DVT

2. Determine risk category:

   • For low/unlikely risk: Perform high-sensitivity D-dimer test
     • If D-dimer negative: DVT excluded (99% negative predictive value) 1
     • If D-dimer positive: Proceed to imaging
   • For moderate risk (in three-tier system):
     • If using high-sensitivity D-dimer and result negative: DVT excluded 1
     • If using moderate-sensitivity D-dimer or positive result: Proceed to imaging
   • For high/likely risk: Proceed directly to imaging regardless of D-dimer 1

3. Imaging approach:

   • Proximal compression ultrasound (CUS) is the preferred initial imaging test 1
   • If proximal CUS is negative but clinical suspicion remains high:
     • Perform either whole-leg ultrasound, repeat proximal CUS in 1 week, or venography 1

Important Considerations and Pitfalls

• Inpatient versus outpatient application: The Wells score performs better in outpatients than inpatients. Studies show poorer discriminatory power in hospitalized patients 2, with higher false-positive rates due to comorbidities.

• Primary care application: The Wells score has been validated in primary care settings with high accuracy 3, though some studies suggest a primary care-specific rule may be slightly more efficient at reducing unnecessary ultrasound referrals 4.

• D-dimer considerations: D-dimer testing has less utility in hospitalized patients or those with conditions that elevate D-dimer (cancer, surgery, trauma, pregnancy, etc.) 1. In these cases, proceed directly to imaging.

• Isolated distal DVT detection: The Wells score performs poorly in predicting isolated distal DVT 5, which may have implications for patients with calf symptoms only.

• Previous DVT history: Although the Wells score includes previous DVT as a criterion, it has not been extensively validated in patients with suspected recurrent DVT 1.

• Age considerations: D-dimer levels increase with age, potentially reducing specificity in elderly patients. Some experts suggest age-adjusted D-dimer cutoffs, though this is not explicitly part of the Wells criteria.

The Wells criteria, when properly applied with appropriate D-dimer testing, can safely exclude DVT in low-risk patients and guide efficient use of ultrasound resources, significantly reducing unnecessary imaging studies by approximately 50% 4.