A detailed evaluation of patients with acute pulmonary embolism and low- or very-low-probability lung scan interpretations.

BACKGROUND To determine the clinical characteristics of patients with pulmonary embolism (PE) and low- or very-low-probability ventilation-perfusion lung scan interpretations. METHODS A retrospective analysis of the data obtained during the Prospective Investigation of Pulmonary Embolism Diagnosis study was performed. The clinical characteristics of patients with acute PE and low- or very-low-probability lung scan interpretation (false-negative interpretations) were compared with patients who had low- or very-low-probability lung scan interpretations and no evidence of acute PE (true-negative interpretations). RESULTS Of the 1493 patients who gave consent to participate in the Prospective Investigation of Pulmonary Embolism Diagnosis study, 399 patients had angiographic or autopsy evidence of acute PE. Pulmonary embolism was excluded in 960 patients. Patients with false-negative lung scan interpretations more commonly had a history of immobilization (P < .0001), trauma to the lower extremities (P < .003), recent surgery (P < .002), or central venous instrumentation (P < .04) compared with patients with true-negative lung scan interpretations. In patients with low- or very-low-probability lung scan interpretations and none of the above-mentioned risk factors, the prevalence of PE was only 4.5%. In contrast, for patients with low- or very-low-probability lung scan interpretations and two or more of the above-mentioned risk factors, the prevalence of PE was 21%. CONCLUSIONS Patients with a history of immobilization, trauma to the lower extremities, recent surgery, or central venous instrumentation were more likely to have false-negative lung scan interpretations. Therefore, this population warrants special attention when deciding on the need for peripheral venous studies or angiography in patients with low- or very-low-probability lung scan interpretation.