EBQ:Wells PE Rule Out

Under Review Journal Club Article
Wells PS et al. "Excluding Pulmonary Embolism at the Bedside without Diagnostic Imaging: Management of Patients with Suspected Pulmonary Embolism Presenting to the Emergency Department by Using a Simple Clinical Model and D-Dimer". Annals of Internal Medicine. 2001. 135(2):98-107.
PubMed Full text PDF

Clinical Question

Is there a simple clinical model along with d-dimer assay testing that can be used to manage patients presenting to the emergency department with suspected pulmonary embolism?


Patients can be safely managed for suspected pulmonary embolism on the basis of pretest probability and d-dimer

Major Points

Wells Criteria

Clinical Features Points
Symptoms of DVT (leg swelling and pain with palpation) 3.0
PE as likely as or more likely than an alternative diagnosis 3.0
HR >100 bpm 1.5
Immobilization for >3 consecutive days or surgery in the previous 4 weeks 1.5
Previous DVT or PE 1.5
Hemoptysis 1.0
Malignancy (receiving treatment, treatment stopped within 6 mon, palliative care) 1.0
Two Tier Wells Score
  • Score 0-4 = PE Unlikely (12.1% incidence of PE)
    • Check D-dimer
      • If D-dimer positive then obtain CTPA or V/Q scan
      • If D-dimer negative, no further workup needed (0.5% incidence of PE at 3 month follow up)
  • Score >4 = PE Likely (37.1% incidence of PE)
    • Obtain CT Pulmonary Angiography or V/Q Scan
  • New evidence suggests lower Wells Score with D-dimer <1000 ng/mL is effective at ruling out PE without imaging

PE exclusion:

  • Low pre-test probability and negative d-dimer
  • Definitive negative imaging needed for moderate and high pretest probability

NPV=99.5% of diagnostic algorithm

Study Design

  • Prospective cohort study in 4 Canadian tertiary care hospitals
  • Patients were evaluated by 1 of 43 designated EM physicians
  • Physician assigned points according to the Well's criteria points table above
  • Primary outcome was development of venous thromboembolic event in patients with excluded PE diagnosis during 3 months of follow-up
    • Diagnosis of PE made with high-probability V-P scan, abnormal result on ultrasound or pulmonary angiography, or VTE during follow-up


Patient Demographics

  • Mean age: 50.5 years old
  • Women: 63%
  • Mean duration of symptoms: 3.2 days
  • Diagnosis of cancer: 7.2%
  • Recent surgery: 8.4%
  • Recent immobilization: 7.6%

Inclusion Criteria

  • Presenting to participating ED
  • Suspicion of PE
  • Symptoms for <30 days
  • Acute onset of new or worsening shortness of breath or chest pain

Exclusion Criteria

  • Suspected DVTof the upper extremity as a likely source of PE
  • No symptoms of PE within 3 days of presentation
  • Anticoagulant therapy for more than 24 hours
  • Expected survival time <3 months
  • Contraindication to contrast media
  • Pregnancy
  • Geographic inaccessibility precluding follow-up
  • <18 years old


Physicians used a clinical model to determine patients’ pretest probability of pulmonary embolism, then performed a D-dimer test

  • Low pretest probability and a negative D-dimer: No further tests, PE excluded
  • All other patients underwent ventilation–perfusion lung scanning
    • If nondiagnostic V-P scan, perform bilateral deep venous ultrasonography
    • Further testing (serial ultrasonography or angiography) was done based on patients' pretest probability and lung scanning results


n=930 patients with suspected pulmonary embolism

Primary Outcome

Pretest Probability Patients Diagnosis of PE
Low 527 7 (1.3%)
Moderate 339 55 (16.2%)
High 64 24 (40.6%)
  • 849 patients had the diagnosis of PE excluded
    • Of these, 5 patients (0.6%) developed PE or DVTduring follow-up. However, 4 of these had not undergone the proper diagnostic protocol.
  • 437 patients had the diagnosis excluded with a negative D-dimer result and low clinical probability
    • Of these, only 1 developed PE during follow-up

Negative predictive value for combined strategy with D-dimer testing: 99.5% (CI, 99.1% to 100%)

Criticisms & Further Discussion

  • Cristopher Study in 2006: algorithm combining clinical probability, D-dimer testing, and computed tomography showed 1.3% incidence of VTE at 3-month follow-up, and 0.5% fatal PE [1]
    • This impact analysis demonstrated that using the Wells criteria in an algorithm with D-dimer and CT can be safely applied as a level 1 decision rule.
  • Clinical gestalt is heavily weighted in this decision rule
    • Having PE as most likely diagnosis automatically classifies the patient as moderate pretest probability
  • D-dimer used had higher specificity and lower sensitivity than industry standard
  • This study used V-P lung scan, which was been replaced by CTA as imaging of choice
    • CTA has increased sensitivity (83%) and specificity (96%), compared to 65% and 94%, respectively, for V-P scan [2]

Relation to PERC rule

  • Wells criteria often used in concert with the PERC rule to increase sensitivity
    • Many argue that the rules shouldn't be applied in parallel because they are not clinically different (they look at many of the same things)
  • Can Wells be considered a rule out criteria?
    • This decision rule study was not designed or validated to be used that way, and further studies must be completed in order for the data to support that application
    • The low pretest probability group in this study had 1.3% diagnosis of PE, suggesting to some that post hoc analysis supports the use of Wells to rule out diagnosis of PE
  • PERC was created to help rule out diagnosis of PE, with a test threshold of 1.8%[3]
    • Using this threshold, some suggest that because the prevalence of PE in the low probability group of the Wells study was well below the test threshold proposed by Kline et all, that PE may be safely excluded in low probability patients without further testing. However, this has not been validated. (see Pulmonary Embolism Video for further discussion)


Grant from the Heart and Stroke Foundation of Nova Scotia and Ontario

See Also

External Links


  1. van Belle, A et al. Effectiveness of Managing Suspected Pulmonary Embolism Using an Algorithm Combining Clinical Probability, D-Dimer Testing, and Computed Tomography. JAMA. 2006;295(2):172-179.
  2. Stein PD, et al. "Multidetector Computed Tomography for Acute Pulmonary Embolism". The New England Journal of Medicine. 2006. 354(22):2317-2327.
  3. Kline JA1, Mitchell AM, Kabrhel C, Richman PB, Courtney DM. Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism.J Thromb Haemost. 2004 Aug;2(8):1247-55.