Estimating the pretest probability threshold to justify empiric administration of heparin prior to pulmonary vascular imaging for pulmonary embolism.

Expertly interpreted pulmonary vascular imaging (either ventilation-perfusion scan or computed tomography chest angiography) is not uniformly available at most hospitals, including those in the US. When evaluating a patient with suspected pulmonary embolism during times when pulmonary vascular imaging is not available, clinicians frequently face the decision of whether to administer heparin while awaiting availability of imaging. In this report, we analyze published data to quantitate the probability of death or disability from untreated pulmonary embolism versus the probability of serious bleeding for one, two and seven days of heparin therapy. For these three time points, we estimate the pretest probability of pulmonary embolism to justify the empiric administration of heparin.