Potential for inter-observer and intra-observer variability in x-ray review to establish stone-free rates after lithotripsy.
The potential for variability among observers interpreting diagnostic tests is well known but has not been well established for radiological imaging of urolithiasis. We measured the inter-observer and intra-observer variability in the reporting of plain abdominal films and tomograms from patients who had undergone extracorporeal shock wave lithotripsy (ESWL). Unlabeled copies of the plain abdominal films and tomograms for 58 patients were individually submitted to 3 different radiologists. Selected films from 25 patients were resubmitted to the same radiologists. We found differences among radiologists reporting plain abdominal films alone 52% of the time and even by the same radiologist rereading the films 24% of the time. Tomograms alone decreased the uncertainty but differences still occurred among radiologists 24% of the time and with themselves 16% of the time. When plain abdominal films and tomograms were read together there were differences among radiologists 28% of the time and with themselves 7% of the time but these were usually minor. We concluded from this study that the plain abdominal film alone was frequently difficult to interpret, resulting in uncertainty about the presence or absence of residual stone fragments. Tomograms alone or a plain abdominal film plus tomograms is superior to a plain abdominal film alone. Finally, radiological assessment with all modalities probably overestimates stone-free rates after ESWL even without consideration of the potential for reporting variability among observers.