Very Low Probability Interpretation of V/Q Lung Scans in Combination with Low Probability Objective Clinical Assessment Reliably Excludes Pulmonary Embolism: Data from PIOPED II

Abstract

Use of a very low probability interpretation of ventilation/perfusion (V/Q) lung scans, if verified by prospective evaluation to have a low positive predictive value (PPV), will reduce the number of nondiagnostic interpretations of V/Q scans and may be particularly useful in patients with a relative contraindication to CT. The purpose of this investigation was to test the hypothesis that a very low probability interpretation of the V/Q scan has a PPV of Methods: Data are from PIOPED II (Prospective Investigation of Pulmonary Embolism Diagnosis II). Very low probability criteria are (a) nonsegmental perfusion abnormalities, (b) perfusion defect smaller than corresponding radiographic lesion, (c) ≥2 matched V/Q defects with regionally normal chest radiograph, (d) 1–3 small segmental perfusion defects (Results: A very low probability consensus interpretation of the V/Q scan was made in 56% of patients. The PPV of a very low probability interpretation of the V/Q scans was 36 of 440 patients (8.2%). Among patients with suspected pulmonary embolism who had a low clinical probability objective clinical assessment and a very low probability V/Q scan, the PPV was 8 of 259 patients (3.1%). Among women ≤40 y, the PPV of the very low probability V/Q with a low objective clinical assessment was 1 of 50 (2%). Conclusion: The very low probability V/Q scan together with a low probability clinical assessment reliably excludes pulmonary embolism.