The Diagnosis of Pulmonary Embolism
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Although clinical diagnosis of pulmonary embolism (PE) is not sufficiently reliable to determine management, it is valuable for stratifying patients into high, intermediate, and low clinical suspicion of embolism. Clinical assessment can then be combined with lung scanning to identify groups of patients with a sufficiently high or low probability of PE that a decision to anticoagulate or withhold therapy can be made. Approximately half of patients with suspected PE will fall into one of these categories. Thrombosis in the deep veins of the leg (DVT) can be detected by noninvasive tests in approximately 50%, and by bilateral venography in approximately 70% of patients with PE, and provides grounds for anticoagulation of some patients with nondiagnostic combinations of clinical and lung scan assessments. Failure to detect DVT makes it less likely but does not exclude the possibility that the patient had a PE. Preliminary evidence suggests that the majority of patients with nondiagnostic combinations of clinical assessment, lung scanning, and negative noninvasive tests for DVT can safely be managed without anticoagulation, provided serial noninvasive tests for DVT remain normal over a 2-week period. Pulmonary angiography may be advisable in patients with nondiagnostic combinations of the above tests in whom (a) the probability of PE remains high (e.g. 30-80%), (b) cardiopulmonary reserve is poor, (c) serial follow-up is not feasible, or (d) future management (e.g. subsequent pregnancy) would be influenced by the result. D-Dimer measurements are sensitive but nonspecific for PE and therefore may have a high negative predictive value, further simplifying the diagnostic approach to PE.
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