What is the approach to rule out pulmonary embolism (PE) in patients?

Pulmonary Embolism Rule-Out Algorithms

Use validated clinical prediction rules (Wells or revised Geneva score) to stratify pretest probability, then apply PERC criteria for low-risk patients or obtain age-adjusted D-dimer testing to safely exclude PE without imaging. 1, 2

Step 1: Assess Pretest Probability

Begin by stratifying patients into low, intermediate, or high probability categories using either validated clinical decision rules or experienced clinician gestalt. 1

Clinical Prediction Rules

• Wells Score assigns points for clinical DVT signs, PE as likely as alternative diagnosis, heart rate >100 bpm, immobilization/surgery, previous PE/DVT, hemoptysis, and malignancy, yielding PE prevalence of 6% (low), 23% (intermediate), and 49% (high probability). 3

• Revised Geneva Score assigns points for previous PE/DVT, heart rate >75 bpm, surgery/fracture within one month, hemoptysis, active cancer, unilateral lower-limb pain, pain on deep venous palpation with unilateral edema, and age >65 years, with PE prevalence of 9% (low), 26% (intermediate), and 76% (high probability). 3, 4

• Simplified Geneva Score assigns one point to each variable (rather than weighted points), making it easier to memorize and use in clinical practice, with similar safety and efficiency to the original Geneva score. 4

• Clinical gestalt by experienced clinicians performs equally well or better than formal prediction rules, with an AUC of 0.81 compared to 0.71 for Wells and 0.66 for revised Geneva score, though agreement between methods is poor. 5

Step 2: Apply PERC Criteria for Low Probability Patients

For patients with low pretest probability (<15%), apply all 8 PERC criteria to identify those who need no further testing. 1, 2

PERC Criteria (All 8 Must Be Met)

• Age <50 years 1, 2
• Pulse <100 bpm 1, 2
• Oxygen saturation >94% on room air 1, 2
• No hemoptysis 1, 2
• No estrogen use 1, 2
• No prior DVT or PE 1, 2
• No unilateral leg swelling 1, 2
• No recent trauma or surgery requiring hospitalization within 4 weeks 1, 2

If all 8 PERC criteria are met, the risk of PE is lower than the risks of testing—do not order D-dimer or imaging. 1, 2 The pooled sensitivity of PERC is 97% with only 0.3% (44 of 14,844 cases) of PEs missed when properly applied. 1

Critical Pitfall

PERC should only be applied to patients already assessed as having low pretest probability (<15%). 2, 6 Do not use PERC as a screening tool in unselected patients, as this increases unnecessary D-dimer testing rather than decreasing it. 1

Step 3: D-Dimer Testing Strategy

For low probability patients who fail any PERC criterion, or for all intermediate probability patients, obtain high-sensitivity D-dimer as the initial diagnostic test. 1, 2

Age-Adjusted D-Dimer Thresholds

• For patients >50 years old, use age-adjusted cutoffs (age × 10 ng/mL) rather than the generic 500 ng/mL threshold. 1, 2 This increases the proportion of patients in whom PE can be excluded from 6.4% to 30% without additional false-negative findings. 1, 2

• For patients ≤50 years old, use the standard cutoff of <500 ng/mL. 1

If D-dimer is below the age-adjusted cutoff, PE is excluded—do not obtain imaging. 1, 2 The negative predictive value is sufficient with posttest probability of PE less than 1.85%. 7

Important Limitation

D-dimer has extremely limited utility in hospitalized patients due to frequent elevation from comorbid conditions, recent surgery, infection, cancer, and inflammation—fewer than 10% of hospitalized patients will have a negative D-dimer. 2 In these patients, proceed directly to imaging if clinical suspicion warrants. 2

Step 4: Imaging for High Probability or Positive D-Dimer

For patients with high pretest probability (>40%), proceed directly to CT pulmonary angiography (CTPA) without D-dimer testing, as a negative D-dimer will not obviate the need for imaging. 1, 2

Imaging Modality Selection

• CTPA is the preferred imaging modality with sensitivity >95% for segmental or larger emboli and specificity of 96%. 2, 7 CTPA also provides alternative diagnoses if PE is not present. 2

• Reserve ventilation-perfusion (V/Q) scans for patients with contraindication to CTPA (renal insufficiency, contrast allergy), pregnancy, younger patients to minimize radiation, or when CTPA is unavailable. 1, 2 V/Q scanning has sensitivity of 85% and specificity of 93% but is diagnostic in only 30-50% of cases. 2

Additional Testing Considerations

• For high probability patients with negative CTPA where clinical concern persists, consider additional testing such as lower extremity venous ultrasound or V/Q scan before definitively ruling out PE, as CTPA false-negative rates range from 5.3% to 40%. 2

• Lower extremity venous ultrasound can be used as initial imaging in patients with obvious signs of DVT, relative contraindications to CT, pregnant patients, or those with history of multiple prior CTs for PE, with diagnostic yield of 30-50%. 2

Special Considerations for Hemodynamically Unstable Patients

For patients with systolic blood pressure <90 mm Hg or shock, perform bedside echocardiography immediately if CTPA is not immediately available or the patient is too unstable for transport. 2 Initiate IV unfractionated heparin with weight-adjusted bolus immediately without waiting for imaging confirmation. 2

Common Pitfalls to Avoid

• Do not apply PERC to patients with moderate or high pretest probability. 2, 6
• Do not order D-dimer in high probability patients—proceed directly to imaging. 1, 2
• Do not use D-dimer as a screening test in hospitalized patients where it has minimal utility. 2
• Do not delay imaging in symptomatic patients with intermediate probability and positive D-dimer. 2
• PE is easily missed in elderly patients, those with severe cardiorespiratory disease, or when the only symptom is isolated dyspnea. 1