What is the workup for a suspected pulmonary embolism?

Workup for Pulmonary Embolism

Begin by stratifying clinical probability using a validated prediction rule (Wells or revised Geneva score), then proceed with D-dimer testing in low/intermediate probability patients or direct imaging in high-risk patients—never order D-dimer in hemodynamically unstable patients or those with high clinical probability. 1

Initial Assessment and Risk Stratification

Hemodynamic Status (First Priority)

• Immediately assess for shock or hypotension (systolic BP <90 mmHg or drop ≥40 mmHg for >15 minutes) to identify high-risk PE requiring emergent management 1
• In hemodynamically unstable patients, perform bedside echocardiography or emergency CTPA depending on availability—initiate IV unfractionated heparin with weight-adjusted bolus (80 units/kg) without delay 1, 2
• Massive PE is highly likely when patients present with collapse, unexplained hypoxia, engorged neck veins, or right ventricular gallop 2

Clinical Probability Assessment (Stable Patients)

• Use Wells score or revised Geneva score to categorize patients into low, intermediate, or high clinical probability 1
• Wells score assigns points for: active cancer (+1), paralysis/recent immobilization (+1), bedridden >3 days or major surgery within 4 weeks (+1.5), localized leg tenderness (+1), entire leg swelling (+1), calf swelling >3 cm (+1), pitting edema (+1), collateral superficial veins (+1), previous PE/DVT (+1.5), heart rate >100 (+1.5), hemoptysis (+1), and PE as likely or more likely than alternative diagnosis (+3) 1
• Revised Geneva score includes: previous PE/DVT (+3), heart rate 75-94 (+3) or ≥95 (+5), surgery or fracture within past month (+2), hemoptysis (+2), active cancer (+2), unilateral leg pain (+3), and pain on deep venous palpation/unilateral edema (+4) 1, 2
• Document respiratory rate in all patients—tachypnea >20 breaths/min is present in most PE cases and significantly raises probability 2, 3

Diagnostic Algorithm by Clinical Probability

Low Clinical Probability

• Apply PERC (Pulmonary Embolism Rule-Out Criteria) first in low-risk patients: if all 8 criteria are met (age <50, pulse <100, SaO₂ ≥95%, no hemoptysis, no estrogen use, no prior DVT/PE, no unilateral leg swelling, no surgery/trauma requiring hospitalization within 4 weeks), the risk of PE is lower than testing risks—stop workup 1
• If PERC criteria not met, order highly sensitive D-dimer (preferably Vidas ELISA or equivalent) 1
• D-dimer <500 ng/mL (or age-adjusted: age × 10 ng/mL for patients >50 years) safely excludes PE—no imaging needed, with 3-month thromboembolic risk <1% 1, 2, 4
• If D-dimer elevated, proceed to CTPA 1

Intermediate Clinical Probability

• Order D-dimer testing (do not use PERC criteria in this group) 1
• D-dimer <500 ng/mL (or age-adjusted) excludes PE—no imaging required 1
• If D-dimer elevated, proceed to CTPA 1
• Initiate therapeutic anticoagulation immediately while awaiting imaging results 1, 2

High Clinical Probability

• Proceed directly to CTPA without D-dimer testing—negative D-dimer does not safely exclude PE in this population 1
• Initiate therapeutic anticoagulation immediately before imaging confirmation 1, 2

Imaging Studies

CT Pulmonary Angiography (CTPA)

• CTPA is the first-line imaging modality for hemodynamically stable patients 1
• A normal CTPA in patients with low or intermediate clinical probability definitively excludes PE—no further testing needed 1
• CTPA showing segmental or more proximal filling defect in intermediate/high probability patients confirms PE 1
• In high clinical probability patients with negative CTPA, consider additional testing (leg ultrasound or pulmonary angiography) or specialist consultation 2

Ventilation-Perfusion (V/Q) Scanning

• Use V/Q scan when CTPA is contraindicated (renal failure, contrast allergy, pregnancy) or unavailable 1
• V/Q scan is preferred in younger patients and pregnant women to minimize radiation exposure, particularly breast tissue 1
• Normal perfusion scan excludes PE 1
• High-probability scan with high clinical probability confirms PE 1, 2
• Low-probability scan with low clinical probability excludes PE 2
• All other combinations require CTPA or pulmonary angiography for definitive diagnosis 1, 2
• V/Q scanning should only be used when chest X-ray is normal and patient has no significant cardiopulmonary disease—otherwise results are likely non-diagnostic 2

Lower Extremity Compression Ultrasound

• Perform CUS before CT imaging in patients with clinical signs of DVT, renal failure, contrast allergy, or pregnancy 1, 2
• Proximal DVT on ultrasound confirms VTE—treat with anticoagulation without further pulmonary imaging 1
• Normal ultrasound does not exclude PE (only 30-50% of PE patients have detectable DVT)—proceed to lung imaging if D-dimer elevated 1, 2

Critical Pitfalls to Avoid

• Never order D-dimer in high clinical probability patients—sensitivity is too low and negative result will not obviate need for imaging 1
• Never order D-dimer in hospitalized patients with infection, cancer, inflammation, or recent surgery—false-positive rates exceed 90%, making the test clinically useless 2, 5
• Do not use D-dimer as a standalone test—always combine with validated clinical probability assessment 1, 5
• Never rely on normal oxygen saturation to exclude PE—up to 40% of PE patients have normal SaO₂ 2, 3
• Do not perform CT venography as adjunct to CTPA—adds no diagnostic value 1
• Do not use MRA to rule out PE—insufficient validation 1
• Never use positive D-dimer alone to diagnose PE—confirmation with imaging is always required due to poor specificity (35%) 5

Timing of Diagnostic Testing

• Imaging for massive PE must be performed within 1 hour of presentation 2
• Imaging for non-massive PE should be completed within 24 hours of clinical suspicion 2, 3
• If imaging cannot be obtained within 24 hours in intermediate/high probability patients, continue therapeutic anticoagulation until imaging is available 2

Special Populations

Pregnancy

• Use V/Q scan or CTPA (both safe during pregnancy)—V/Q scan preferred by many to minimize fetal radiation 1
• Consider lower extremity ultrasound first to avoid any radiation if DVT can be confirmed 1
• NOACs are contraindicated in pregnancy—use LMWH or unfractionated heparin 1

Cancer Patients

• D-dimer has limited utility due to high false-positive rates 2, 5
• Proceed directly to imaging based on clinical probability 3
• Markedly elevated D-dimer (>5000 μg/L) may indicate occult malignancy in 29% of cases 5