Clinicians' interpretation of the indeterminate ventilation-perfusion scan report

Most patients with suspected pulmonary embolism are initially investigated by radio-nuclide ventilation-perfusion (VQ) scanning. Approximately 70% of VQ scans are "indeterminate". Further investigations should be considered in such patients in order to establish a definitive diagnosis. However, these investigations are rarely requested in patients with indeterminate scans in our institution. We therefore decided to review the casenotes of such patients to determine their subsequent management. Over a 9 month period, 131 (32%) out of a total of 413 consecutive VQ scans were reported as indeterminate. The casenotes of 111 of these patients (65 female, 46 male, mean age 65 years, range 17-91 years) were reviewed. 52 of the 111 patients (46%) were treated on clinical grounds without further investigation; 12 patients (11%) had further investigation; and in 39 of the cases (35%) the VQ scan report was misinterpreted. 20 (38%) of the 52 patients managed on clinical grounds were treated for pulmonary embolus with anticoagulation and 26 (50%) were not anticoagulated. Of the 12 patients who were investigated further, nine had lower limb Doppler ultrasound and three had contrast venography. No patients had pulmonary angiography. Of the 39 cases where the VQ report was misinterpreted, the result was misquoted in the casenotes of 37 (95%) as negative for PE and none of these patients were anticoagulated, and in two cases (5%) it was misquoted as positive for PE and anticoagulant therapy was instituted. The misunderstanding was observed in all clinical firms. Such misinterpretation may have significant implications, since 30-40% of patients with indeterminate scans may have had PE. Our findings suggest that clinicians need to be better informed of the significance of an indeterminate VQ scan result.