What is the first line of diagnosis for a high-risk patient suspected of having a pulmonary embolism (PE), Computed Tomography (CT) chest scan or D-dimer test?

First-Line Diagnostic Approach for Suspected PE in High-Risk Patients

For high-risk patients with suspected pulmonary embolism (PE), CT pulmonary angiography (CTPA) should be the first-line diagnostic test rather than D-dimer testing. 1, 2

Diagnostic Algorithm for Suspected PE

Step 1: Risk Stratification

• Use validated clinical prediction tools (Wells score or Geneva score) to assess pretest probability 2
• Evaluate for key symptoms: dyspnea, chest pain, tachycardia, tachypnea, and hypoxemia

Step 2: Diagnostic Testing Based on Risk

• For high-risk patients:

  • Proceed directly to CTPA without D-dimer testing
  • CTPA is highly sensitive and specific for PE diagnosis 1
  • May also reveal alternative diagnoses explaining the patient's symptoms 1

• For low to intermediate-risk patients:

  • Start with D-dimer testing
  • If D-dimer negative, PE can be safely excluded without imaging 1, 2
  • If D-dimer positive, proceed to CTPA 1
  • For patients >50 years, use age-adjusted D-dimer thresholds (age × 10 ng/mL) 2

Rationale for CTPA as First-Line in High-Risk Patients

1. Diagnostic accuracy: CTPA has established high sensitivity and specificity for PE diagnosis 1, 3
2. Clinical efficiency: Direct CTPA in high-risk patients avoids delays in diagnosis
3. Comprehensive evaluation: CTPA can identify alternative diagnoses when PE is not present 1

Alternative Diagnostic Approaches

• Lower-extremity venous ultrasonography: Consider for patients with multiple prior CT scans or with lower extremity symptoms 2
• V/Q scanning: Option for patients with contraindications to CTPA (renal insufficiency, contrast allergy) 2
  • Note: A normal perfusion scan effectively excludes PE 2

Important Caveats

• D-dimer testing has limited utility in high-risk patients due to high false positive rates
• Negative CTPA is highly reliable for excluding clinically significant PE 3
• The accuracy of older CT technology was more limited, with sensitivities ranging from 0.68-0.81 depending on the level of pulmonary arteries examined 4
• Modern multidetector CT technology has significantly improved diagnostic accuracy compared to older studies 5

Common Pitfalls to Avoid

• Relying on D-dimer alone in high-risk patients can lead to missed diagnoses
• Overreliance on CT scans in low-risk patients with negative D-dimer results is unnecessary 1, 2
• Failure to consider radiation exposure risks in patients requiring multiple imaging studies 2

By following this algorithm, clinicians can efficiently diagnose or exclude PE while minimizing unnecessary testing and radiation exposure.