A Wells Score is a point-based checklist that doctors use to estimate how likely it is that you have a blood clot, either in your leg (deep vein thrombosis, or DVT) or in your lungs (pulmonary embolism, or PE). Based on your total score, your doctor decides whether you need a simple blood test, an imaging scan, or no further workup at all. There are actually two separate Wells Scores: one for DVT and one for PE, each with different criteria and point values.
How the DVT Wells Score Works
The DVT version adds up points from 10 clinical features. Nine of them add one point each, and one subtracts two points. Your doctor evaluates the following:
- Active cancer (treatment within the past 6 months or palliative care): +1
- Paralysis or recent cast on a lower leg: +1
- Bedridden 3+ days or major surgery within the past 12 weeks: +1
- Tenderness along the deep veins of the leg: +1
- Entire leg swelling: +1
- Calf swelling at least 3 cm larger than the other leg: +1
- Pitting edema (skin that holds an indent when pressed) only in the affected leg: +1
- Visible surface veins that aren’t varicose veins: +1
- Previous documented DVT: +1
- Another diagnosis just as likely as DVT: −2
That last item is important. If a doctor thinks your swollen leg is more likely caused by a muscle strain or cellulitis, two points come off your total. This single criterion keeps a lot of people out of the high-risk category.
Scores break into three tiers. A total of 0 or below is low probability (roughly a 10% chance of DVT). A score of 1 to 2 is moderate probability (about 25%). A score of 3 or higher is high probability (around 50%).
How the PE Wells Score Works
The pulmonary embolism version uses seven criteria, and the point values vary more:
- Clinical signs of DVT (leg swelling, pain with palpation): +3
- PE is the most likely or equally likely diagnosis: +3
- Heart rate above 100: +1.5
- Immobilization 3+ days or surgery in the past 4 weeks: +1.5
- Previous PE or DVT: +1.5
- Coughing up blood: +1
- Active cancer (treatment within the past 6 months or palliative): +1
For PE, the three-tier breakdown is: less than 2 points is low probability (about 5%), 2 to 6 is intermediate (about 20%), and above 6 is high probability (roughly 50%). There is also a simplified version of the PE score where each of the seven criteria counts as just one point. In this version, a score of 2 or more classifies you as “PE likely.” The simplified version is easier to calculate and performs comparably in clinical studies.
What Happens After Your Score
The Wells Score doesn’t diagnose anything by itself. It determines the next step in a testing sequence, which saves many patients from unnecessary scans.
If your DVT score is low or moderate (2 or below), you’ll typically get a D-dimer blood test first. D-dimer measures a protein fragment that appears when blood clots break down. A result below 500 ng/mL effectively rules out DVT, and no further testing is needed. A result at or above that threshold leads to a leg ultrasound. If your score is high (3 or above), your doctor skips the blood test entirely and orders an ultrasound right away, because a D-dimer can’t reliably rule out a clot in high-risk patients.
The PE pathway follows a similar pattern. Low or intermediate scores start with a D-dimer test. A negative result rules out PE. A positive result leads to a CT scan of the chest (called CTPA) or, in some cases, a ventilation-perfusion scan. High-probability patients go straight to imaging without waiting for D-dimer results.
This stepwise approach matters because CT scans expose you to radiation and contrast dye, and ultrasounds take time and resources. A simple, inexpensive blood test can safely end the workup for many patients.
Where the Wells Score Falls Short
The scoring system is less reliable in certain groups. Cancer patients are the most notable example. In patients with active cancer, only about 9% score low enough to attempt ruling out DVT with a D-dimer test. Even among those low-scoring cancer patients, 2.2% still turned out to have a clot, which crosses the accepted safety threshold of 2% for missed cases. For this reason, doctors are generally more cautious with cancer patients and may proceed to imaging regardless of score.
Patients with a history of DVT also present a challenge. The original scoring system gives one point for a prior clot, but research from a large individual-patient meta-analysis found that this wasn’t quite enough. The modified version of the Wells rule adds an extra point for previous DVT to improve accuracy in this group. If you’ve had a prior blood clot, your doctor may use this adjusted approach.
The Wells Score was also developed and validated primarily in outpatient settings. Its accuracy in hospitalized patients, who often have multiple competing conditions that could explain their symptoms, is less well established. Hospitalized patients tend to score higher simply because they’re bedridden or post-surgical, which can inflate their risk category without necessarily reflecting a true clot.
Why Doctors Rely on It
Blood clots are common enough to be dangerous but uncommon enough that most people evaluated for one don’t actually have one. Without a structured tool, doctors face a difficult choice: scan everyone (expensive, sometimes harmful) or rely on gut instinct (unreliable). The Wells Score provides a middle path, sorting patients into groups where the actual prevalence of clots ranges from about 5% to 50%, and matching each group to the right level of testing. It’s one of the most widely used clinical decision tools in emergency medicine and has been validated across multiple large studies and patient populations.