What is the diagnostic approach for suspected pulmonary embolism?

Diagnostic Approach for Suspected Pulmonary Embolism

The diagnostic approach for suspected pulmonary embolism should begin with clinical probability assessment using validated tools like the Wells score or revised Geneva score, followed by selective testing with D-dimer for low/intermediate risk patients and immediate imaging for high-risk patients. 1

Clinical Probability Assessment

The first step in diagnosing pulmonary embolism (PE) is determining the pretest clinical probability using either:

• Validated clinical decision tools:
  • Wells score
  • Revised Geneva score
• Clinical gestalt (physician's implicit assessment)

Research shows that clinical gestalt may actually perform better than formal scoring systems, with better discrimination of low and high probability patients 2.

Pulmonary Embolism Rule-Out Criteria (PERC)

For patients with low clinical probability, apply the PERC criteria:

Criteria	Description
Age	< 50 years
Heart rate	< 100 beats/minute
Oxygen saturation	≥ 95%
History of VTE	No
Recent trauma/surgery	No
Hemoptysis	No
Estrogen use	No
Unilateral leg swelling	No

If all 8 PERC criteria are met, the risk of PE is sufficiently low (<0.3%) that no further testing is needed 1, 3.

D-Dimer Testing

• For low probability patients who don't meet all PERC criteria: Order D-dimer test
• For intermediate probability patients: Order D-dimer test
• For high probability patients: Skip D-dimer and proceed directly to imaging 3, 1

Important: Use age-adjusted D-dimer thresholds for patients >50 years:

• Age-adjusted cutoff = age × 10 ng/mL
• This maintains sensitivity >97% while significantly improving specificity 3, 1

A normal D-dimer result safely excludes PE in low and intermediate probability patients, avoiding unnecessary imaging 1.

Imaging Studies

When to Order Imaging:

• High clinical probability patients
• Low/intermediate probability patients with elevated D-dimer

Preferred Imaging Modalities:

1. Computed Tomography Pulmonary Angiography (CTPA):

   • First-line imaging when available and not contraindicated
   • High sensitivity (95%) and specificity (98%)

2. Ventilation-Perfusion (V/Q) Scan:

   • Alternative when CTPA is unavailable or contraindicated
   • A normal perfusion scan reliably excludes PE
   • A high-probability V/Q scan confirms PE 3, 1

3. Ultrasound of Lower Extremities:

   • May be considered in selected patients
   • Finding of proximal DVT confirms PE diagnosis 1

Special Considerations

For High-Risk PE (Shock/Hypotension):

• Emergency CTPA or bedside echocardiography based on availability
• Echocardiography can identify right ventricular dysfunction suggesting PE 1

For Pregnant Patients:

• Modified approach needed
• V/Q scan preferred over CTPA in early pregnancy due to radiation exposure concerns 1

Common Pitfalls to Avoid

1. Skipping clinical probability assessment

   • This determines the entire diagnostic pathway

2. Ordering D-dimer in high probability patients

   • A negative result does not safely exclude PE in this group

3. Failure to use age-adjusted D-dimer thresholds

   • Leads to decreased specificity in older patients

4. Applying PERC criteria to all patients

   • Should only be used for low clinical probability patients 1

5. Overreliance on individual risk factors

   • Many population-level risk factors don't add meaningfully to validated prediction tools 3

By following this evidence-based approach, clinicians can diagnose PE accurately while minimizing unnecessary testing and radiation exposure.