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    Wells' Criteria for Pulmonary Embolism

    Objectifies risk of pulmonary embolism.
    When to Use
    Why Use

    The Wells’ Criteria risk stratifies patients for pulmonary embolism (PE) and provides an estimated pre-test probability. The physician can then chose what further testing is required for diagnosing pulmonary embolism (I.E. d-dimer or CT angiogram).

    The Wells’ Criteria risk stratifies patients for pulmonary embolism (PE), and has been validated in both inpatient and emergency department settings. Its score is often used in conjunctiion with d-dimer testing to evaluate for PE.

    • There must first be a clinical suspicion for PE in the patient (this should not be applied to all patients with chest pain or shortness of breath, for example).
    • Wells' can be used with either 3 tiers (low, moderate, high) or 2 tiers (unlikely, likely). We recommend the two tier model as this is supported by ACEP’s 2011 clinical policy on PE. (See Next Steps)

      • Wells’ is often criticized for having a “subjective” criterion in it (“PE #1 diagnosis or equally likely”)
    • Wells’ is not meant to diagnose PE but to guide workup by predicting pre-test probability of PE and appropriate testing to rule out the diagnosis.
    • The Wells’ Score has been validated multiple times in multiple clinical settings.
      • Physicians have a low threshold to test for pulmonary embolism.
      • The score is simple to use and provides clear cutoffs for the predicted probability of pulmonary embolism.
      • The score aids in potentially reducing the number of CTAs performed on low-risk PE patients.


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    Next Steps
    Creator Insights


    • Some advocate using the Wells’ score over clinician gestalt to predict who is low-risk and then applying the PERC rule to stop workup for PE.
    • As with all clinical decision aids, the physician must first have a suspicion of the diagnosis before attempting to apply the Wells criteria.
    • The original intent of this tool was to determine who was low risk enough to rule out testing with a d-dimer.
    • Age adjusted d-dimer cutoffs have been validated for use in patients over 50 years in low risk patients (rGeneva “not high” or Wells’ low). If using the appropriate d-dimer assay consider calculating the age adjusted d-dimer cutoff of: Age (years) x 10 µg/L = cutoff (for patients > 50 years).
    • While both two and three tier models are accepted, guidelines appear to favor the two tier model which utilizes only the high sensitivity d-dimer and more conservative risk stratification; “intermediate” risk patients are thought to be still too high risk to be evaluated without further risk stratification.


    Three Tier Model

    • Patient is determined to be low risk (<2 points:1.3% incidence PE): consider d-dimer testing to rule out Pulmonary embolism. Alternatively consider a rule-out criteria such as PERC.
      • If the dimer is negative consider stopping workup.
      • If the dimer is positive consider CTA.
    • Patient is determined to be moderate risk (score 2-6 points, 16.2% incidence of PE): consider high sensitivity d-dimer testing or CTA.
      • If the dimer is negative consider stopping workup.
      • If the dimer is positive consider CTA.
    • Patient is determined to be high risk (score >6 points: 37.5% incidence of PE): consider CTA. D-dimer testing is not recommended.

    Two Tier Model

    • Patient risk is determined to be “PE Unlikely” (0-4 points, 12.1% incidence of PE): consider high sensitivity d-dimer testing.
      • If the dimer is negative consider stopping workup.
      • If the dimer is positive consider CTA.
    • Patient risk is determined to be “PE Likely” (>4 points, 37.1% incidence of PE): consider CTA testing.

    Critical Actions

    • Given the next generation d-dimer high sensitivity but low specificity (approx 50%), patients who are considered high risk should be ruled out with CTA.
    • Never delay resuscitative efforts for diagnostic testing, especially in the unstable patient.
    • History and exam should always be performed prior to diagnostic testing.


    Addition of the selected points:

    Facts & Figures

    Score interpretation:

    Score Risk Category
    Three-Tier Model
    0 - 1 Low Risk
    2 - 6 Moderate Risk
    >6 High Risk
    Two Tier Model
    ≤4 PE Unlikely (with d-dimer)
    ≥5 PE Likely (with CTA)

    Evidence Appraisal

    • The original Wells study was performed on cohorts where prevalence of PE was high: approximately 30%. Two further emergency department studies validated this tool with a 9.5%-12% PE prevalence.
    • The largest study demonstrated risk stratification with:
      • Low score of 1-2 having a 1.3% prevalence.
      • Moderate score of 2-6 having a 16.2% prevalence.
      • High score of >6 having a 37.5% prevalence.
    • The Christopher study divided the Wells scoring system into 2 categories:
      • A score of 4 or less was defined as “PE unlikely” and tested with a d-dimer.
      • A score of 5 or more was defined as “PE likely” and went straight to CTA
    • Overall Incidence of PE was 12.1% in the “unlikely” group vs. 37.1% in the “likely” group.
    • If dimer was negative no further testing was performed.
    • If dimer was positive the patient went to CTA.
    • 20.4% of all patients who went to CTA had a diagnosis of PE.
    • In the “PE unlikely” group, those with a negative dimer and discharged to home had an incidence of missed PE on 3 month follow up of 0.5% .


    Dr. Phil Wells

    From the Creator

    Dr. Wells on use of his scores for MDCalc:

    The model should be applied only after a history and physical suggests that venous thromboembolism is a diagnostic possibility. it should not be applied to all patients with chest pain or dyspnea or to all patients with leg pain or swelling. This is the most common mistake made. Also, never never do the D-dimer first [before history and physical exam]. The monster in the box is that the D-dimer is done first and is positive (as it is for many patients with non-VTE conditions) and then the physician assumes that VTE is now possible and then the model is done. Do the history and physical exam first and decide if VTE is a diagnostic possibility!

    Dr. Wells on testing in medicine for MDCalc:

    The importance of Clinical pretest probability is underutilized in medicine. Recognizing the power of a simple concept, derived essentially from Bayes theorem, that discordance between the clinical PTP and the test result should raise suspicion of a false negative test (if high PTP) or false positive test (if low PTP), we sought to derive prediction rules for suspected DVT and for suspected PE. Used appropriately these rules will improve patient care.

    About the Creator

    Phil Wells, MD, MSc, is a professor and chief of the Department of Medicine at The University of Ottawa. He is also on the faculty of medicine and a senior scientist at the Ottawa Hospital Research Institute. Dr. Wells researches thromboembolism, thrombophilia and long term bleeding risk in patients on anticoagulants.

    To view Dr. Phil Wells's publications, visit PubMed

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    Dr. Phil Wells
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