The clinical diagnosis of pulmonary embolism is highly nonspecific because none of the symptoms or signs of pulmonary embolism is unique and all may be caused by other cardiorespiratory disorders. Thus, objective testing is mandatory to either confirm or exclude a diagnosis of pulmonary embolism. Based on current available information, a diagnostic approach for the management of clinically suspected pulmonary embolism is proposed. After a history and physical examination, electrocardiogram and chest X-ray film, all patients should undergo perfusion lung scanning. The finding of a normal perfusion lung scan rules out clinically significant pulmonary embolism, and anticoagulant therapy is withheld. The management of patients with an abnormal perfusion lung scan is more complex. If this scan demonstrates one or more segmental (or greater) perfusion defects, ventilation lung scanning should be performed because the probability of pulmonary embolism is markedly increased if a mismatch is found, with a high probability scan (positive predictive value 86%) providing an end point for commencing anticoagulant therapy in the majority of patients. In an abnormal ventilation-perfusion study, the presence of a ventilation-perfusion match does not rule out the possibility of pulmonary embolism, and further objective testing is required in these patients with nonhigh probability scans. Similarly, in patients with small perfusion defects (one or more subsegmental defects) or indeterminate lung scan findings (in which the perfusion scan defects correspond to a defect on a chest X-ray film), the predictive values obtained from these ventilation-perfusion scan patterns are not sufficiently high or low to confirm or exclude the presence of pulmonary embolism.(ABSTRACT TRUNCATED AT 250 WORDS)
