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Calculate the Wells score to estimate the probability of deep vein thrombosis (DVT) and guide diagnostic workup.
Wells Score
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Risk Category
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| Wells Score | Risk Level | DVT Probability |
|---|---|---|
| ≤0 | Low | ~5% |
| 1-2 | Moderate | ~17% |
| ≥3 | High | ~53% |
The Wells score for DVT is a clinical prediction rule used to estimate the pretest probability of deep vein thrombosis. Developed by Dr. Philip Wells, it combines clinical signs, symptoms, and risk factors to stratify patients and guide diagnostic testing decisions.
The Wells score helps determine whether a patient requires imaging (ultrasound) or can be safely evaluated with D-dimer testing alone. In low to moderate probability patients, a negative D-dimer can rule out DVT without the need for ultrasound. High probability patients should proceed directly to imaging.
D-dimer is a sensitive but non-specific marker of thrombosis. When combined with Wells score risk stratification, it becomes a powerful tool. In low to moderate risk patients (Wells ≤2), a negative high-sensitivity D-dimer has a negative predictive value exceeding 99%, safely ruling out DVT without imaging.
The "alternative diagnosis" criterion requires clinical judgment - it should only be checked if another diagnosis is equally or more likely than DVT. This criterion carries significant weight (-2 points) and can change management. Examples include cellulitis, muscle strain, or Baker's cyst rupture.
Use the Wells score whenever DVT is suspected based on symptoms like leg swelling, pain, or warmth. It should be calculated before ordering diagnostic tests to guide appropriate workup and avoid unnecessary imaging.
Measure both calves at 10 cm below the tibial tuberosity (the bony prominence below the kneecap). A difference of more than 3 cm between the symptomatic and asymptomatic leg counts as positive for this criterion.
Bilateral symptoms make assessment more challenging. The Wells score was developed for unilateral symptoms. In bilateral cases, consider the more symptomatic leg, but clinical judgment and imaging may be needed regardless of score.
A low Wells score alone does not rule out DVT. You must also obtain a D-dimer test. Only if both the Wells score is low (≤2) AND the D-dimer is negative can you safely exclude DVT without imaging.
Active cancer includes patients currently receiving treatment, those who received treatment within the past 6 months, or those receiving palliative care. Cancer in remission for more than 6 months without treatment does not count.
The Wells score has been extensively validated. When properly applied with D-dimer testing, it can safely exclude DVT in about 30-40% of patients without imaging. The negative predictive value approaches 99% when both Wells score and D-dimer are negative.
Initial ultrasound can miss DVT, especially proximal propagating clots. With high Wells score and negative initial ultrasound, consider repeat ultrasound in 5-7 days. Some guidelines recommend serial imaging for high-risk patients with negative initial studies.
In high probability patients (Wells ≥3) with no contraindications, empiric anticoagulation while awaiting imaging is reasonable if imaging cannot be obtained promptly. This decision should consider bleeding risk and time to imaging availability.