How should pulmonary embolism be diagnosed?

Use validated clinical prediction rules (Wells, Geneva) to stratify pre-test probability. PE-unlikely + negative age-adjusted D-dimer excludes PE. PE-likely or positive D-dimer: proceed to CTPA. V/Q scan if contrast contraindicated or renal impairment. Lower extremity ultrasound if DVT suspected. High clinical suspicion: begin anticoagulation pending imaging. Hemodynamically unstable: bedside echo for RV strain, consider empiric thrombolysis.