What is the initial step in working up a suspected pulmonary embolism (PE)?

Working Up Suspected Pulmonary Embolism

The initial step in working up suspected PE is to assess clinical probability using a validated decision rule or clinical gestalt, followed by selective D-dimer testing in low-to-intermediate risk patients, with imaging reserved for those who remain at risk after this stratification. 1

Step 1: Clinical Probability Assessment

All patients with possible PE must have their clinical probability formally assessed and documented before any testing. 1

Recognize Classic Presentations

• Sudden collapse with raised jugular venous pressure (faintness and/or hypotension) 1
• Pulmonary hemorrhage syndrome (pleuritic pain and/or hemoptysis) 1
• Isolated dyspnea (no cough, sputum, or chest pain) 1

Common Pitfalls in Recognition

PE is easily missed in three specific scenarios: 1

• Patients with severe pre-existing cardiorespiratory disease
• Elderly patients
• When the only symptom is breathlessness without other features

Key Clinical Features to Document

• Respiratory rate >20/min (present in most PE patients and should be recorded in all cases) 1
• Tachypnea, dyspnea, or hypoxemia (if all three are absent, PE can be excluded) 1
• Age and risk factors (PE is rare if age <40 with no risk factors) 1

Risk Factor Assessment

Score +1 point if other diagnoses are unlikely on clinical grounds and after basic investigations (chest X-ray, ECG, arterial blood gas). 1

Score +1 point if any major risk factor is present: 1

• Recent immobilization or major surgery
• Recent lower limb trauma and/or surgery
• Clinical deep vein thrombosis
• Previous proven DVT or PE
• Pregnancy or postpartum
• Major medical illness

Step 2: Apply PERC Rule in Low-Risk Patients

In patients with low pretest probability (<15%), use the Pulmonary Embolism Rule-out Criteria (PERC) to identify those who need no further testing. 1

If ALL 8 PERC criteria are met, the likelihood of PE is 0.3% and no further testing is required (sensitivity 97%): 1

• Age <50 years
• Heart rate <100/min
• Oxygen saturation >94%
• No recent surgery or trauma
• No prior venous thromboembolism
• No hemoptysis
• No unilateral leg swelling
• No estrogen use

Do not apply PERC to intermediate or high-risk patients. 1

Step 3: D-Dimer Testing Strategy

D-dimer should only be ordered after clinical probability assessment, and should NOT be performed in high-risk patients who require immediate imaging. 1

When to Use D-Dimer

• Low-risk patients who do not meet all PERC criteria 1
• Intermediate-risk patients 1

D-Dimer Interpretation

A negative D-dimer (<500 ng/mL) reliably excludes PE in low and intermediate probability patients using high-sensitivity assays (SimpliRED, Vidas, MDA), and no imaging is needed. 1

Use age-adjusted D-dimer thresholds in patients ≥50 years old: age × 10 ng/mL (maintains sensitivity >97% while significantly improving specificity from 14.7% to 35.2% in patients >80 years). 1

Critical Caveat

Each hospital must provide information on the sensitivity and specificity of its specific D-dimer assay. 1

Step 4: Imaging Selection

For Non-Massive PE (Hemodynamically Stable)

CT pulmonary angiography (CTPA) is the recommended initial lung imaging modality. 1, 2

A good quality negative CTPA excludes PE and requires no further investigation or treatment. 1

Imaging should ideally be performed within 24 hours in non-massive PE. 1

Alternative: Isotope Lung Scanning

May be considered as initial imaging ONLY if ALL of the following are met: 1

• Facilities available on-site
• Chest radiograph is normal
• No significant symptomatic concurrent cardiopulmonary disease
• Standardized reporting criteria are used
• Non-diagnostic results will be followed by further imaging

A normal isotope scan reliably excludes PE, but high-probability results have a significant false-positive rate. 1

For Massive PE (Hemodynamically Unstable)

CTPA or echocardiography will reliably diagnose clinically massive PE, and imaging should be performed within 1 hour. 1

Special Consideration: Leg Ultrasound

In patients with coexisting clinical DVT, leg ultrasound as the initial test is often sufficient to confirm venous thromboembolism without lung imaging. 1

However, a single normal leg ultrasound should not be relied upon to exclude subclinical DVT. 1

Step 5: Anticoagulation Timing

Heparin should be started immediately in patients with intermediate or high clinical probability BEFORE imaging is obtained. 1, 3

Use weight-based unfractionated heparin: 80 units/kg bolus, then 18 units/kg/hour infusion, targeting aPTT 1.5-2.5 times control. 1, 3

Critical Pitfall to Avoid

Delaying anticoagulation while awaiting diagnostic confirmation significantly increases mortality. 3

Basic Investigations Required in All Suspected PE

Perform these in all patients with suspected PE: 1

• Chest radiography (to assess for alternative diagnoses and guide V/Q scan interpretation)
• ECG (may show signs of right heart strain)
• Arterial blood gas (hypoxemia supports diagnosis but is not specific)

Always consider and actively seek alternative diagnoses at presentation and when PE is excluded. 1