Better Care for Patients with Suspected Pulmonary Embolism

The diagnosis and treatment of pulmonary embolism engage the internist as few other diseases do, for many good reasons. Physicians often miss the diagnosis (1). The mortality rate for untreated pulmonary embolism is quite high (2, 3) and is much lower when the disorder is correctly treated (4). However, treatment-related bleeding carries a substantial fatality rate (5). Pulmonary angiography, still the definitive test, is inconvenient to do at night, and the sensitivity of noninvasive imaging tests is still too low to rule out disease when clinical suspicion is high (6).

The medical literature contains 2 lines of inquiry regarding the diagnosis of pulmonary embolism. The first is the pragmatic management trial, which asks how often pulmonary embolism occurs when low-risk patients do not receive anticoagulant therapy. The second is concerned with estimating the pretest probability of pulmonary embolism and with using data related to test accuracy to calculate the post-test probability. The foundation is the Bayes theorem, which states that the post-test odds of a disease equal the pretest odds multiplied by the likelihood ratio of the test result. This relationship tells us that the interpretation of a test result depends on the pretest odds of disease.

When should we withhold treatment? Some would say only when the probability of pulmonary embolism is zero. This policy will lead us to perform expensive tests in patients with a very low probability of pulmonary embolism. Decision theory states that we should withhold treatment when the probability of pulmonary embolism is lower than the treatment threshold probability for pulmonary embolism, which is the lowest probability at which it is reasonable to treat.

This issue of Annals includes 2 articles about the management of pulmonary embolism. One reports that physicians often withhold anticoagulant treatment after a negative test result when …