Suspected pulmonary embolism is one of the most common diagnostic questions in the ED and on the wards, and one of the easiest to get wrong in both directions. Scan everyone and you bury patients in radiation, contrast, and incidental findings. Scan too few and you miss a diagnosis that kills.
The Wells score for PE is how most clinicians split that difference. It turns your clinical suspicion into a pretest probability, and that probability decides the next test: a D-dimer, or straight to CT pulmonary angiography. Here are the criteria, how to score and interpret it, a worked example, and the mistakes that make it fail.
Wells score criteria for PE
Clinical signs and symptoms of DVT (leg swelling, pain with palpation of the deep veins)
PE is the most likely diagnosis, or equally likely
Immobilization ≥3 days, or surgery in the previous 4 weeks
Active malignancy (treatment within 6 months, or palliative)
Total possible score: 0 to 12.5. The Wells score for DVT is a different rule with different criteria; don't mix them up.
Wells score interpretation
There are two ways to read the total. Most current pathways use the two-tier version, sometimes called the modified Wells score, because it maps directly onto a testing decision.
Two-tier (modified Wells): PE likely vs unlikely
D-dimer. Negative rules out PE; positive goes to CTPA.
CT pulmonary angiography. Skip the D-dimer.
Three-tier (original Wells): low, moderate, high
Consider PERC; if PERC-negative, no further testing
D-dimer; positive goes to CTPA
Either version works if you use it consistently. The two-tier model is simpler and is what most order sets and the ACP and ACEP pathways are built around.
How to calculate it: a worked example
A 62-year-old woman is two weeks out from a knee replacement. She has new pleuritic chest pain and dyspnea, a heart rate of 112, and nothing else explains it better than PE.
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Surgery in the previous 4 weeks: 1.5
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PE is the most likely diagnosis: 3
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Total: 6, which is PE likely on the two-tier model
She goes straight to CT pulmonary angiography. A D-dimer adds nothing here; even a negative result would not be enough to rule out PE at this pretest probability.
The clinical workflow
1.
Ask whether PE is actually on your differential. The Wells score is for patients you already suspect, not a screening tool for everyone with chest pain.
2.
If your gestalt is low, apply the PERC rule first. If all 8 PERC criteria are negative, stop; no D-dimer needed.
3.
Calculate the Wells score.
4.
PE unlikely (≤4): order a D-dimer. Negative rules out PE. Positive goes to CTPA.
5.
PE likely (>4): go straight to CTPA. If CTPA is contraindicated, consider V/Q scanning or lower-extremity ultrasound.
6.
Unstable patient: none of this applies. Bedside echo and empiric treatment decisions come first.
Wells and PERC: how they work together
PERC and Wells answer different questions. PERC asks whether you need to test at all. Wells asks which test comes next. PERC only applies when your clinical gestalt for PE is already low, roughly under 15 percent. A patient is PERC-negative only if every one of these is true:
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Oxygen saturation 95% or higher on room air
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No unilateral leg swelling
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No surgery or trauma requiring hospitalization in the past 4 weeks
If any PERC criterion is positive, PERC can't rule anything out, and you move on to the Wells score.
Make the D-dimer work harder
A fixed D-dimer cutoff of 500 ng/mL loses specificity with age, which means more negative scans in older patients. Two validated adjustments help:
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Age-adjusted D-dimer: for patients over 50, use age × 10 ng/mL (FEU) as the cutoff in PE-unlikely patients. A 75-year-old's cutoff becomes 750. ACEP and ACP both support this approach.
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YEARS algorithm: if none of three items is present (signs of DVT, hemoptysis, PE most likely), a D-dimer under 1,000 ng/mL rules out PE; with one or more, the cutoff stays at 500. Your institution may use YEARS instead of Wells.
Where the Wells score goes wrong
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The "PE most likely" item is subjective, and it carries 3 points. Two clinicians can score the same patient a 3 or a 6. Decide honestly whether another diagnosis explains the picture better.
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Ordering a D-dimer in PE-likely patients. A negative D-dimer does not rule out PE when the Wells score is above 4. Go to imaging.
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Using it on everyone with chest pain. Scoring patients you never suspected inflates testing; that is what PERC and gestalt are for.
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Applying it in pregnancy. The Wells score wasn't validated in pregnant patients; pregnancy-adapted YEARS is the better-studied option.
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Forgetting it in inpatients. The Wells score was validated mostly in outpatients and ED patients; it performs less well in hospitalized patients, who score points for immobilization and malignancy more often.
The takeaway
The Wells score doesn't diagnose PE. It decides your next test. Use PERC to avoid testing low-risk patients, Wells to choose between D-dimer and imaging, and an age-adjusted D-dimer to avoid scanning older patients who don't need it. The rule is only as good as your honesty on the 3-point "most likely diagnosis" item.
Wells, PERC, and the rest of the PE workup in one place
DUK-C puts the Wells score, PERC, and the PE treatment protocols that come after the scan in one app, so you aren't switching between a calculator site and a guideline PDF mid-workup. The protocol library is free; the calculators are part of a one-time premium unlock. If the scan is positive in a patient with cancer, our
cancer-associated thrombosis algorithm picks up from there, and for undifferentiated chest pain, start with the
chest pain algorithm.
Less searching. More medicine. Download DUK-C free on the App Store.
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