Scenario

On inpatient teaching rounds, we recently discussed the admission of a 45 year old woman with chest pain. This patient presented to the emergency department after an episode of chest pain lasting approximately 30 minutes. The pain was pleuritic in nature, located on the right side of her chest, and was associated with shortness of breath. The patient reported no palpitations, diaphoresis, nausea, or vomiting. She had no relevant medical history, was taking oral contraceptives, and had no family history of cardiac or thromboembolic disease. Her vital signs, including oxygen saturation, were normal, as were the physical examination results. The working diagnosis was pulmonary embolus (PE), and she was started on intravenous heparin and scheduled for a ventilation-perfusion (V/Q) scan to be done within the next half hour.

After interviewing the patient with a team (2 residents, 3 interns, and 2 medical students) and reviewing the data, I asked the team to individually record their best estimate of the probability that this patient had PE. At first, the team was reluctant, in particular the third year residents, but with encouragement all members of the team scribbled down their best estimate. The probabilities were reviewed and were found to range from 5% to 80%.

The importance of accurately determining the pre-test probability of disease is highlighted in figure 1. For our patient, resident 1 estimated the patient’s pre-test probability of PE …