New methods for estimating pretest probability in the diagnosis of pulmonary embolism.

The clinical assessment of the probability of pulmonary embolism is a key step in proposed diagnostic strategies for pulmonary embolism, because the interpretation of noninvasive test results is conditional on the pretest probability derived from the presence or absence of clinical factors. The past year has brought important progress in the general area of clinical prediction of pulmonary embolism with the publication of two new simple clinical prediction rules. Each of the prediction rules includes a total of seven clinical variables that, when combined, allow for the categorization of patients into categories of low, intermediate, or high pretest probability of pulmonary embolism. Although these clinical prediction rules are perhaps only slightly better than the estimates of experienced clinicians, they provide an explicit method for estimating the probability of PE as an adjunct to diagnostic testing. Further validation work is now needed to assess how well these new prediction rules perform in settings other than the derivation sites.