What is the initial workup for a suspected pulmonary embolism (PE)?

Initial Workup for Suspected Pulmonary Embolism

Begin with clinical probability assessment using a validated prediction rule (Wells score or revised Geneva score), then apply PERC criteria if low probability, or obtain D-dimer testing for low-to-intermediate probability patients, proceeding directly to CT pulmonary angiography (CTPA) only in high probability cases. 1

Step 1: Clinical Probability Assessment

Stratify pretest probability using either the Wells score, revised Geneva score, or experienced clinical gestalt—all perform equivalently with sensitivity of 97% and specificity of 22%. 1

The revised Geneva score assigns points for:

• Previous PE/DVT
• Heart rate >75 bpm (3 points) or 75-94 bpm (5 points)
• Recent surgery or fracture within 1 month
• Hemoptysis
• Active malignancy
• Unilateral lower limb pain
• Pain on deep venous palpation with unilateral edema
• Age >65 years 2, 1

This categorizes patients into low (10% PE prevalence), intermediate (30%), or high (~65%) probability groups. 3

Step 2: Apply PERC Rule (Low Probability Patients Only)

For patients with low pretest probability (<15%), apply all eight Pulmonary Embolism Rule-Out Criteria (PERC)—if all are met, PE is safely excluded without further testing. 1

All eight PERC criteria must be satisfied:

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

If even one PERC criterion is violated, proceed to D-dimer testing. 1

Step 3: D-Dimer Testing Strategy

Obtain high-sensitivity D-dimer in patients with low pretest probability who fail PERC criteria, or in all patients with intermediate pretest probability—sensitivity 96%, specificity 35%. 1

Age-Adjusted D-Dimer Thresholds

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

• If D-dimer is negative (<500 ng/mL or below age-adjusted threshold), PE is excluded—no further testing needed. 2, 3
• If D-dimer is positive, proceed to CTPA. 3

Critical Caveat About D-Dimer

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, 1 In this population, proceed directly to imaging rather than obtaining D-dimer.

Step 4: Imaging Selection

High Pretest Probability Patients

Proceed directly to CTPA without D-dimer testing in high probability patients, as a negative D-dimer will not obviate the need for imaging—sensitivity 83%, specificity 96%. 1

CT Pulmonary Angiography (CTPA)

CTPA is the primary imaging modality for hemodynamically stable patients with positive D-dimer or high clinical probability, with sensitivity >95% for segmental or larger emboli. 1 CTPA provides the additional benefit of identifying alternative diagnoses such as pneumonia, aortic dissection, or cardiac pathology. 1

Important Limitation of CTPA in High-Risk Patients

The false-negative rate of CTPA alone in clinically high-risk patients ranges from 5.3% to 40%—consider additional testing (lower extremity venous ultrasound, V/Q scan) after a negative CTPA in high probability patients before definitively ruling out PE. 2

For patients with intermediate pretest probability and negative CTPA where clinical concern persists, consider lower extremity venous ultrasound as an additional test. 2

Alternative Imaging: Venous Ultrasound

When venous ultrasound is performed as initial imaging and shows DVT in a patient with symptoms consistent with PE, this confirms VTE disease and may preclude the need for additional diagnostic imaging. 2

Consider venous ultrasound as initial imaging in:

• Patients with obvious signs of DVT
• Relative contraindications to CT (borderline renal insufficiency, contrast allergy)
• Pregnant patients (especially first trimester)
• Patients with history of multiple prior CTs for PE 2

Alternative Imaging: V/Q Scanning

Reserve ventilation-perfusion (V/Q) scanning for patients with contraindication to CTPA, younger patients to minimize radiation, or when CTPA is unavailable—sensitivity 85%, specificity 93%. 1 However, V/Q scanning is diagnostic in only 30-50% of cases, often yielding non-diagnostic results requiring further testing. 2, 1

Step 5: Hemodynamically Unstable Patients (High-Risk PE)

In patients with shock or hypotension, perform bedside echocardiography immediately if CTPA is not immediately available or the patient is too unstable for transport. 2, 3

• If echocardiography shows RV overload/dysfunction, consider emergency reperfusion treatment. 2
• If echocardiography is negative for RV dysfunction, this practically excludes PE as the cause of hemodynamic instability—search for alternative causes (tamponade, acute valvular dysfunction, aortic dissection). 2
• Initiate IV unfractionated heparin with weight-adjusted bolus immediately without waiting for imaging confirmation. 3

Common Pitfalls to Avoid

Do not use D-dimer as a screening test in high probability patients—it has low negative predictive value in this population and will not change management. 1

Do not apply PERC criteria to patients with moderate or high clinical probability—PERC was validated only for low probability emergency department patients. 1

Do not delay imaging while waiting for troponin results, as PE and acute coronary syndrome can coexist. 1

Develop institutional protocols for patients with recurrent symptoms and history of multiple CTs for PE—5% of patients evaluated for PE will have 5 or more CTs within 5 years. 2 Consider lower extremity ultrasound or V/Q scanning as alternatives to repeated CT exposure.