Inter- and intraradiologist variability in the BI-RADS assessment and breast density categories for screening mammograms

Objective: The aim of this study was to evaluate reader variability in screening mammograms according to the American College of Radiology Breast Imaging Reporting and Data System (BI-RADS) assessment and breast density categories. Methods: A stratified random sample of 100 mammograms was selected from a population-based breast cancer screening programme in Barcelona, Spain: 13 histopathologically confirmed breast cancers and 51 with true-negative and 36 with false-positive results. 21 expert radiologists from radiological units of breast cancer screening programmes in Catalonia, Spain, reviewed the mammography images twice within a 6-month interval. The readers described each mammography using BI-RADS assessment and breast density categories. Inter-and intraradiologist agreement was assessed using percentage of concordance and the kappa (kappa) statistic. Results: Fair interobserver agreement was observed for the BI-RADS assessment [kappa = 0.37, 95% confidence interval (CI) 0.36-0.38]. When the categories were collapsed in terms of whether additional evaluation was required (Categories III, 0, IV, V) or not (I and II), moderate agreement was found (kappa = 0.53, 95% CI 0.52-0.54). Intra-observer agreement for BI-RADS assessment was moderate using all categories (kappa = 0.53, 95% CI 0.50-0.55) and substantial on recall (kappa = 0.66, 95% CI 0.63-0.70). Regarding breast density, inter-and intraradiologist agreement was substantial (kappa = 0.73, 95% CI 0.72-0.74 and kappa = 0.69, 95% CI 0.68-0.70, respectively). Conclusion: We observed a substantial intra-observer agreement in the BI-RADS assessment but only moderate interobserver agreement. Both inter-and intra-observer agreement in mammographic interpretation of breast density was substantial. Advances in knowledge: Educational efforts should be made to decrease radiologists' variability in BI-RADS assessment interpretation in population-based breast screening programmes.