A 58-year-old man with a history of recent hip fracture surgery presents to the emergency department with acute onset dyspnea, pleuritic chest pain, and tachycardia (HR 110/min). Clinical suspicion for pulmonary embolism is high. His D-dimer is elevated at 2.5 µg/mL. Which investigation is most appropriate to confirm the diagnosis?

## Investigation of Choice for Suspected PE **Key Point:** CTPA (computed tomography pulmonary angiography) is the gold standard and first-line confirmatory test for pulmonary embolism in hemodynamically stable patients with high clinical suspicion and elevated D-dimer. ### Why CTPA? 1. **High sensitivity and specificity**: >95% sensitivity and >95% specificity for PE detection [cite:Harrison 21e Ch 297] 2. **Speed and availability**: Rapid acquisition (seconds), widely available in most hospitals 3. **Anatomical detail**: Allows visualization of clot location (central vs. peripheral) and assessment of right ventricular strain 4. **Prognostic information**: Can identify massive PE and guide management intensity ### Clinical Context This patient has: - High pretest probability (recent immobilization, surgery, acute symptoms) - Elevated D-dimer (rules out low-risk group) - Hemodynamic stability (suitable for CTPA) **High-Yield:** In a hemodynamically unstable patient with high clinical suspicion, treatment may begin empirically while awaiting CTPA, or bedside echocardiography may be used to assess RV dysfunction as a surrogate marker. ### Diagnostic Algorithm for PE ```mermaid flowchart TD A[Suspected PE]:::outcome --> B{Clinical probability?}:::decision B -->|Low| C[D-dimer]:::action C -->|Negative| D[PE excluded]:::outcome C -->|Positive| E[CTPA]:::action B -->|Intermediate/High| F{Hemodynamically stable?}:::decision F -->|Yes| E F -->|No| G[Bedside echo + empiric anticoagulation]:::action E --> H{PE confirmed?}:::decision H -->|Yes| I[Anticoagulation/IVC filter]:::action H -->|No| J[Alternative diagnosis]:::outcome ``` **Clinical Pearl:** A negative D-dimer in low-risk patients effectively excludes PE; however, D-dimer is nonspecific and elevated in many conditions (inflammation, malignancy, recent surgery), so it must be paired with clinical assessment.