A 58-year-old man with a 3-day history of acute dyspnea, pleuritic chest pain, and tachycardia (HR 110/min) is admitted. Clinical suspicion for pulmonary embolism is high. His D-dimer is elevated at 2.5 μg/mL (normal <0.5). Which investigation is most appropriate to confirm the diagnosis?

Explanation

## Investigation of Choice for Pulmonary Embolism Confirmation **Key Point:** CT pulmonary angiography (CTPA) is the gold standard and first-line confirmatory test for suspected pulmonary embolism in hemodynamically stable patients with elevated clinical probability. ### Why CTPA is Preferred 1. **High sensitivity and specificity** — >95% sensitivity for PE detection, especially for central and lobar emboli 2. **Rapid acquisition** — can be performed within minutes, critical in acute presentations 3. **Anatomic visualization** — directly visualizes thrombus in pulmonary arteries 4. **Additional diagnostic yield** — can identify alternative diagnoses (pneumonia, aortic dissection, pneumothorax) when PE is excluded 5. **Widely available** — most hospitals have MDCT capability ### Role of D-Dimer in PE Workup **High-Yield:** D-dimer is a screening tool, NOT diagnostic. An elevated D-dimer (as in this case) indicates need for imaging confirmation, not diagnosis itself. D-dimer is used to rule out PE in low-probability patients (negative D-dimer = PE unlikely); a positive D-dimer mandates imaging. ### Comparison of Investigations | Investigation | Sensitivity | Specificity | Role | Limitations | |---|---|---|---|---| | **CTPA** | >95% | >95% | Gold standard, first-line | Radiation, contrast nephropathy | | **V/Q scan** | 80–90% | 80–90% | Alternative if CTPA contraindicated | Nonspecific; requires normal CXR | | **Echocardiography** | 50–60% | Variable | Assesses RV strain, hemodynamics | Not diagnostic for PE; used for risk stratification | | **Chest X-ray** | Low | Low | Exclude alternative diagnoses | Cannot diagnose PE; may show wedge-shaped opacity | ### Clinical Pearl **Clinical Pearl:** In hemodynamically **unstable** patients (shock, syncope), bedside echocardiography may be performed first to assess RV dysfunction and guide immediate management (thrombolysis/embolectomy), but CTPA remains the definitive diagnostic test once stabilized. ### Algorithm for PE Investigation ```mermaid flowchart TD A[Suspected PE]:::outcome --> B{Clinical probability}:::decision B -->|Low| C[D-dimer]:::action C -->|Negative| D[PE ruled out]:::outcome C -->|Positive| E[CTPA]:::action B -->|Intermediate/High| E E -->|PE confirmed| F[Anticoagulation]:::action E -->|PE excluded| G[Alternative diagnosis]:::outcome B -->|Hemodynamically unstable| H[Bedside echo + CTPA]:::urgent H --> I[Consider thrombolysis]:::urgent ``` [cite:Harrison 21e Ch 297]