What is the protocol for ruling out pulmonary embolism (PE)?

Protocol for Ruling Out Pulmonary Embolism (PE)

The optimal protocol for ruling out pulmonary embolism involves risk stratification, followed by selective use of D-dimer testing and appropriate imaging based on pretest probability. 1

Initial Risk Stratification

• Assess pretest probability using validated clinical decision tools or clinical judgment 1
• Consider major risk factors: recent immobility, major surgery, lower limb trauma/surgery, pregnancy/postpartum, major medical illness, previous VTE 1
• Use Wells score or simplified revised Geneva score to classify patients into risk categories 1, 2
• Low probability = no risk factors; Intermediate = one risk factor; High = multiple risk factors 1

Low Pretest Probability Patients

• Apply PERC (Pulmonary Embolism Rule-out Criteria) to patients with low pretest probability 2, 3
• PERC criteria (all must be negative): age <50 years, heart rate <100 bpm, oxygen saturation ≥95% on room air, no unilateral leg swelling, no hemoptysis, no recent trauma/surgery, no prior VTE, no hormone use 2
• If all PERC criteria are negative in a low-risk patient, PE can be safely ruled out without further testing (miss rate only 0.3%) 2, 3
• If any PERC criterion is positive, proceed to D-dimer testing 1, 2

D-dimer Testing

• Use D-dimer testing for patients with low or intermediate pretest probability who don't meet PERC criteria 1
• D-dimer should NOT be performed if: alternative diagnosis is highly likely, clinical probability is high, or in probable massive PE 1
• Use age-adjusted D-dimer thresholds (age × 10 ng/mL) for patients >50 years instead of generic 500 ng/mL cutoff 1
• A negative D-dimer in low/intermediate risk patients effectively rules out PE without need for imaging 1

Imaging Studies

• CT pulmonary angiography (CTPA) is the preferred imaging modality for patients with high pretest probability or positive D-dimer 1
• Reserve ventilation-perfusion (V/Q) scans for patients with contraindications to CTPA (renal insufficiency, contrast allergy) or when CTPA is unavailable 1
• Normal CTPA in low/intermediate risk patients effectively rules out PE 1
• For high-risk patients with negative CTPA, consider additional testing (venous ultrasound, conventional pulmonary angiography) 1

Venous Ultrasound

• Consider venous ultrasound as initial imaging in patients with obvious signs of DVT, contraindications to CTPA, or pregnancy 1
• A positive finding of DVT on ultrasound in a patient with symptoms consistent with PE can establish VTE diagnosis without additional imaging 1
• Consider lower extremity venous ultrasound as an additional test for patients with intermediate/high pretest probability and negative CTPA 1

Special Considerations

• For suspected massive PE with hemodynamic instability, perform bedside echocardiography or emergency CTPA and initiate immediate IV heparin 1
• In pregnant patients, consider venous ultrasound as initial imaging to avoid radiation exposure 1
• For patients with borderline renal function or contrast allergy, V/Q scan or venous ultrasound may be preferred over CTPA 1

Common Pitfalls to Avoid

• Don't use D-dimer as a routine "screening" test for all patients with respiratory symptoms 1, 2
• Don't perform D-dimer testing in patients with high clinical probability 1
• Don't apply PERC criteria to patients with intermediate or high pretest probability 2
• Don't rely solely on CTPA in high-risk patients without additional testing if CTPA is negative 1
• Don't routinely perform CT venography as an adjunct to CTPA 1