The PIOPED II criteria for ventilation perfusion studies breaks down the probability of pulmonary embolus into high, intermediate, low, very low probabilities, as well as a normal scan. One of the criteria for very low probability is a triple-match defect in the upper and middle lungs zones - i.e. a matched defect on the ventilation and perfusion study with correlative chest radiograph findings. The positive predictive value of this finding is approximately 4%. However, a triple matched defect in the lower lung zone is of intermediate probability. [PubMed REF] Click for HyperLink

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