The problems of the clinical and laboratory diagnosis of pulmonary embolism.

Suspecting and diagnosing venous thrombosis and pulmonary embolism remain major clinical problems. For a variety of reasons, including the patient's pre-existing cardiac and pulmonary status and the release of humoral mediators, pulmonary emboli evoke varied responses in different patients. Symptoms and signs of pulmonary embolism are not specific; they depend on the size and the hemodynamic and humoral consequences of the embolus. Conversely, they may not be present at all. Chest radiographic and electrocardiographic findings are nonspecific, and may be most helpful in establishing the presence of other conditions that may be confused with pulmonary embolism. Arterial blood gases can only heighten the suspicion of pulmonary embolism; they should never be used to exclude the diagnosis. Clinical and laboratory findings therefore do not diagnose pulmonary embolism; rather, they raise the level of concern and set the stage for the performance of subsequent diagnostic studies.