Review of criteria appropriate for a very low probability of pulmonary embolism on ventilation-perfusion lung scans: A position paper

The "low-probability" interpretation of ventilation-perfusion lung scans ha s been characterized as misleading or even dangerous because of the high pr evalence of pulmonary embolism associated with such an interpretation. Sinc e the completion of the Prospective Investigation of Pulmonary Embolism Dia gnosis (PIOPED) study, analyses of the PIOPED database have allowed identif ication of several abnormalities seen on ventilation-perfusion scans that h ave a positive predictive value (PPV) for pulmonary embolism of less than 1 0%, These include nonsegmental perfusion abnormalities (PPV = 8%), perfusio n defects smaller than the corresponding areas of increased opacity at ches t radiography (PPV = 8%), matched ventilation-perfusion abnormalities in tw o or three zones of a single lung (PPV = 3%), one to three small segmental perfusion defects (PPV = 1%), triple matched defects in the upper or middle lung zone (PPV = 4%), and the stripe sign (PPV = 7%). Use of these abnorma lities as interpretative criteria constitutes "very low probability" interp retation and will reduce the number of low-probability interpretations of v entilation-perfusion lung scans, which may be considered nondiagnostic beca use of the unacceptably high rate of false-negative results. This will enha nce the utility of the ventilation-perfusion lung scan for screening patien ts with suspected pulmonary embolism.