Audit analysis of inter-observer variability and accuracy of different criteria in the interpretation of intermediate lung ventilation and perfusion (VQ) scan

Objectives To assess the degree of inter-observer variation and accuracy of different criteria in the interpretation of Lung VQ scan.

Methods Eight-seven VQ scans were reported as intermediate probability using PIOPED criteria. An independent professional unaware of the original report, reported the same scans using simple criteria for interpretation. The diagnostic classification of VQ scan obtained for an independent professional were analysed against CTPA scan.

Results Eighty-seven VQ scans were reported as intermediate probability. Independent observer reported the number of normal, low and high probability categories as 14(16%), 68(78%) and 5(6%) respectively. Out of 87, 62 patients underwent CTPA scan. Out of 9 normal VQ scans; 8 had a negative CTPA and 1 had an equivocal result. Out of 48 with a low probability scan; 38 had a negative CTPA scan, 9 had a positive CTPA scan and 1 had an equivocal result. Out of 5 with a high probability scan; 3 had a negative CTPA scan and 2 had a positive CTPA scan. The area under the curve (AUC) of the receiver operating characteristics (ROC) curve for independent observer was 0.760. Kappa value is 0.44.

Conclusions There was a significant variation in the interpretation of VQ scan between the two interpretations. Using simple criteria it is possible to improve the accuracy of reporting when compared to CTPA used as the gold standard. This approach reduces cost and unnecessary radiation exposure, and more prompt diagnosis