Efforts to improve interobserver agreement in histopathological grading

The present study aimed to assess the interobserver variation in histopathological grading of 88 slides by four experienced pathologists who, before the start of the study, reached consensus about the method of grading through a joint session behind a discussion microscope. The results were compared with two previous studies, the first assessing the observer variation under normal conditions, the second doing the same after theoretical agreement about which morphological characteristics were relevant for grading. In the present study the pathologists first made a provisional diagnosis on low power view, followed by a final diagnosis on high power view, scoring various morphological characteristics as in the second study. The unweighted and weighted group kappa values for the final diagnosis were 0.41 and 0.71 respectively in the present study (after the consensus meeting), compared to 0.33 and 0.70 respectively in the second study (after only theoretical consensus), and 0.28 and 0.55 in the first study (without consensus). We conclude that a consensus meeting appears to be useful to improve the interobserver agreement.