Wells’ Criteria for Pulmonary Embolism

Why Use

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.

When to 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).

Formula

Pearls / Pitfalls

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 conjunction 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.

Management

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.

Advice

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) × 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.

More Information

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)