Needle in a Haystack

A 63-year-old man presented to the emergency department with shortness of breath that had begun the evening before, after he had gone to bed, and worsened progressively during the night. He had had no fevers, chills, cough, hemoptysis, chest pain, or peripheral edema and had no history of congestive heart failure. Five months earlier, a pulmonary embolus had been diagnosed, for which he received warfarin maintenance therapy; the results of prothrombin-time testing, expressed as an international normalized ratio, were consistently above 2.0.