What are the diagnostic steps and treatment options for pulmonary thromboembolism (PTE)?

Diagnosing Pulmonary Thromboembolism

Begin with clinical probability assessment using validated scoring systems (Wells or Geneva), then proceed with D-dimer testing in low/intermediate probability patients, followed by CT pulmonary angiography (CTPA) as the definitive imaging test of choice. 1

Initial Clinical Assessment and Risk Stratification

Hemodynamic Status Determines Diagnostic Urgency

• Immediately assess for hemodynamic instability (shock, hypotension with systolic BP <90 mmHg, or need for vasopressors) as this defines high-risk PE and alters the diagnostic pathway 1, 2
• In hemodynamically unstable patients with high clinical probability, perform bedside echocardiography immediately if CT is not available; right ventricular overload on echo is sufficient to justify PE-specific treatment without further testing 1, 2
• Do not delay treatment while awaiting imaging in unstable patients with high clinical suspicion 1, 3

Clinical Probability Assessment (For Stable Patients)

• Use either a three-level scheme (low, intermediate, high probability) or two-level scheme (PE unlikely vs. PE likely) to stratify clinical probability 1, 2
• The Wells score and Geneva score are validated tools for this assessment 4, 5
• This step is critical as it determines whether D-dimer testing is appropriate 1

D-Dimer Testing Strategy

When to Use D-Dimer

• Measure D-dimer only in patients with low or intermediate clinical probability, or those classified as "PE unlikely" 1, 2
• Do not measure D-dimer in high clinical probability patients (Class III recommendation) as it will not change management 1
• Consider using age-adjusted cut-offs (age × 10 μg/L for patients >50 years) or cut-offs adapted to clinical probability as alternatives to fixed thresholds 2

Interpreting D-Dimer Results

• If D-dimer is negative in low/intermediate probability patients, reject the diagnosis of PE without further testing (3-month thromboembolic risk <1%) 1, 2
• If D-dimer is elevated (≥500 μg/L), proceed to imaging 2
• Important caveat: D-dimer has limited utility in hospitalized patients due to high prevalence of conditions causing elevation (infection, cancer, inflammation, recent surgery) 2

Imaging for Definitive Diagnosis

CT Pulmonary Angiography (First-Line)

• CTPA is the imaging test of first choice for patients with elevated D-dimer or high clinical probability 1, 2
• Accept the diagnosis of PE if CTPA shows segmental or more proximal filling defects 1
• CTPA is accurate, widely available, and can identify alternative diagnoses 4, 6
• Dual-energy CT with iodine mapping provides additional perfusion information and may enhance diagnostic accuracy 7

Ventilation-Perfusion (V/Q) Scanning (Alternative)

• V/Q scintigraphy is a valid option when CTPA is contraindicated (e.g., contrast allergy, renal impairment, pregnancy) 1, 2
• If perfusion lung scan is normal, reject the diagnosis of PE without further testing 1
• V/Q SPECT may be considered and offers lower radiation exposure than CTPA, particularly beneficial in younger patients and pregnancy 2, 4
• Limitation: Non-diagnostic (intermediate probability) V/Q scans occur in approximately 24% of cases and require further investigation 2

Lower Extremity Venous Ultrasonography

• If proximal compression ultrasonography (CUS) shows deep vein thrombosis (DVT), this confirms venous thromboembolism and justifies treatment without need for pulmonary imaging 2
• This approach is particularly useful when CTPA is contraindicated or unavailable 2
• If CUS is positive, proceed with risk assessment to guide PE management 2

Tests NOT Recommended

• Do not perform CT venography as routine adjunct to CTPA (Class III recommendation) 1
• Do not use MR angiography to rule out PE (Class III recommendation) as it lacks sufficient validation 1

Diagnostic Algorithm for Non-Massive PE (Hemodynamically Stable)

1. Assess clinical probability using validated scoring system 1
2. If low/intermediate probability: Measure D-dimer 1
   • If D-dimer <500 μg/L: Stop—PE excluded 2
   • If D-dimer ≥500 μg/L: Proceed to step 3
3. If high clinical probability OR elevated D-dimer: Perform CTPA 1
   • If CTPA shows segmental/proximal filling defect: PE confirmed—treat 1
   • If CTPA negative: PE excluded 1
   • If CTPA contraindicated: Perform V/Q scan or lower extremity ultrasound 1, 2

Diagnostic Algorithm for Massive PE (Hemodynamically Unstable)

1. Assess hemodynamic status immediately 1
2. If CT immediately available: Perform emergency CTPA 2
3. If CT not immediately available: Perform bedside echocardiography 1, 2
   • If RV overload present: Initiate PE-specific treatment immediately (thrombolysis or embolectomy) 1, 2
   • If no RV overload: Search for alternative cause of shock 2
4. Do not delay treatment for diagnostic confirmation in unstable patients with high clinical suspicion 1

Critical Pitfalls to Avoid

• Never order D-dimer in high clinical probability patients—it wastes time and a positive result doesn't change management 1
• Don't rely on D-dimer in hospitalized patients—specificity is too low (<10% will have negative D-dimer) 2
• Don't use normal lung scan or CTPA to exclude massive PE if clinical suspicion remains extremely high—though exceedingly rare, case reports exist of massive PE with normal imaging 2
• Don't perform pulmonary angiography routinely—it has been replaced by CTPA in modern practice 2, 6
• Don't delay anticoagulation while awaiting diagnostic tests in patients with high clinical probability unless bleeding contraindications exist 3, 8