Utility of lower extremity venous ultrasound scanning in the diagnosis andexclusion of pulmonary embolism in outpatients

Study objective: Emergency physicians frequently rely on normal findings fr om a lower extremity Venous ultrasound examination as a method to decrease the probability of pulmonary embolism (PE) in outpatients with a nondiagnos tic ventilation-perfusion lung scan (V/Q scan). The objective of this study was to evaluate the diagnostic utility of bilateral lower extremity venous ultrasound scanning in the diagnosis of PE in emergency department patient s with a low-, moderate-, or indeterminate-probability (nondiagnostic) V/Q scan. Methods: This prospective, 2-center, descriptive study was conducted at the EDs of 2 large teaching hospitals. From an initial cohort of 570 nonreferr ed outpatients, a convenience sample of 156 patients who had both a nondiag nostic V/Q scan and a lower extremity venous ultrasound scan performed was selected as the study population. The sensitivity and specificity for a sin gle lower extremity venous ultrasound scan and the posttest probability of PE were determined for the study population. Results: In the study population, the best-case sensitivity of the lower ex tremity venous ultrasound scan for PE was 54% (95% confidence interval [Cl] 37% to 71%) and the specificity was 98% (95% Cl 94% to 100%). The likeliho od ratio of a positive test result was 27. The likelihood ratio of a negati ve test result was 0.49, yielding a lowest possible posttest probability of PE of 12% (95% Cl 6% to 17%). Conclusion: This study demonstrates that the combination of a nondiagnostic (low, moderate, or indeterminate) V/Q scan plus a single negative result f rom lower extremity venous ulrrasound examination, even in a best-case scen ario, does not exclude the diagnosis of PE.