Suspected pulmonary embolism. The difficulties of diagnostic evaluation

It is impossible to prove or disprove a diagnosis of acute pulmonary embolism on clinical grounds. Diagnostic evaluation is best carried out by first attempting to identify a provable alternative diagnosis that can explain a patient's symptoms. Once the diagnosis of pulmonary embolism is seriously considered, a ventilation-perfusion (V/Q) scan is the next step. A positive ("high-probability") or negative ("normal-perfusion") scan is an appropriate diagnostic end point. Unfortunately, most V/Q scans are nondiagnostic, and the workup must be pursued further. Color-flow (duplex) ultrasound, if available, is the next logical step. If a site of deep venous thrombosis cannot be identified, pulmonary angiography is indicated. Newer methods, such as D-dimer measurement and spiral computed tomography, are being studied.