What is the Wells score for Deep Vein Thrombosis (DVT) and how is it used in diagnosis and treatment?

Wells Score for Deep Vein Thrombosis

The Wells score is a validated clinical prediction rule that stratifies patients into risk categories for DVT and should be used in combination with D-dimer testing to determine which patients require venous ultrasound imaging. 1

Components of the Wells Score

The Wells score assigns points based on the following clinical characteristics 1:

• Active cancer (treatment within 6 months or palliative care): 1 point 1
• Paralysis, paresis, or recent plaster immobilization of lower extremities: 1 point 1
• Recently bedridden ≥3 days or major surgery within 12 weeks requiring general/regional anesthesia: 1 point 1
• Localized tenderness along the deep venous system distribution: 1 point 1
• Entire leg swollen: 1 point 1
• Calf swelling ≥3 cm larger than asymptomatic side (measured 10 cm below tibial tuberosity): 1 point 1
• Pitting edema confined to symptomatic leg: 1 point 1
• Collateral superficial veins (nonvaricose): 1 point 1
• Previously documented DVT: 1 point 1
• Alternative diagnosis at least as likely as DVT: -2 points 1

Risk Stratification and DVT Prevalence

Three-Tier System

The original Wells score categorizes patients into three probability groups 1:

• Low probability (score ≤0): DVT prevalence 5.0% (95% CI, 4%-8%) 1
• Moderate probability (score 1-2): DVT prevalence 17% (95% CI, 13%-23%) 1
• High probability (score ≥3): DVT prevalence 53% (95% CI, 44%-61%) 1

Two-Tier System

A modified version uses a simplified dichotomous approach 1:

• DVT unlikely (score <2): DVT prevalence 6% (95% CI, 4%-8%) 1
• DVT likely (score ≥2): DVT prevalence 28% (95% CI, 24%-32%) 1

Clinical Application Algorithm

For Patients with Low/Unlikely Pretest Probability (Score <2)

Step 1: Calculate Wells score before ordering imaging 1

Step 2: If score <2, obtain high-sensitivity D-dimer testing 1, 2

Step 3: If D-dimer is negative, DVT is safely excluded without ultrasound (negative predictive value 99.5%) 2

Step 4: If D-dimer is positive despite low Wells score, proceed to venous ultrasound 1

For Patients with Likely Pretest Probability (Score ≥2)

Proceed directly to venous ultrasound without D-dimer testing, as the pretest probability is sufficiently high to warrant imaging 1

Special Populations

Cancer patients: Proceed directly to compression ultrasonography without using Wells score or D-dimer testing, as D-dimer is frequently elevated in malignancy and lacks specificity 3

Imaging Recommendations

Complete duplex ultrasound (CDUS) is the preferred diagnostic test, which includes compression of deep veins from inguinal ligament to ankle (including posterior tibial and peroneal veins), bilateral common femoral vein spectral Doppler waveforms, popliteal spectral Doppler, and color Doppler images 1

• Compression should be performed at 2-cm intervals 1
• Limited protocols examining only proximal veins require repeat scanning at 5-7 days to safely exclude distal DVT that may propagate proximally 1
• Proximal compression ultrasound has sensitivity 93.2%-95.0% and specificity 93.1%-94.4% for proximal DVT 1

Important Limitations and Pitfalls

Interobserver reliability concerns: While one study confirmed reproducibility among resident physicians, the Wells score has not been widely evaluated for interobserver agreement 1

Performance varies by setting: The Wells score performs less well in primary care settings and hospitalized patients compared to emergency department populations 1, 4

Poor performance for isolated distal DVT: Both the original and modified Wells scores perform poorly in predicting isolated distal (calf) DVT 4

Subjective elements: The Wells score contains subjective components, particularly the "-2 points for alternative diagnosis" criterion, which requires clinical judgment 1

D-dimer limitations in hospitalized patients: D-dimer testing has reduced utility in acutely ill or hospitalized patients due to high false-positive rates from conditions like malignancy, infection, surgery, trauma, pregnancy, and inflammatory conditions 1

Asymptomatic DVT: Approximately one-third of patients with DVT are asymptomatic, limiting the sensitivity of any clinical prediction rule 1, 3

Clinical Outcomes

Safety of withholding anticoagulation: In patients with low Wells score and negative D-dimer who do not undergo imaging, the frequency of symptomatic DVT or PE during 3-month follow-up is acceptably low at 1.2% (95% CI, 0.2%-4.4%) 1

Benefits of anticoagulation: The benefits of anticoagulation therapy in patients with proximal DVT clearly outweigh risks in preventing pulmonary embolism and post-thrombotic syndrome 1