Trends in the utilization of mammography in Washington state and British Columbia: relation to stage of diagnosis and mortality.

To compare the utilization of an imaging technology in the United States and Canada and its effect on clinical outcomes, trends in the utilization of mammography among women aged 50 to 75 years from 1984 through 1988 in Washington State and British Columbia were examined. Also compared were trends in the stage at time of diagnosis of invasive breast cancer and mortality due to breast cancer in the two regions. Annual mammography use increased in both regions, but the proportion of women examined was consistently two to three times higher in Washington than in British Columbia (43% vs 16% in 1988). Although there was no difference in mortality trends, the proportion of women diagnosed with localized disease in Washington increased each year (from 52% to 64%, P less than .001), while in British Columbia it remained unchanged at approximately 56%. Results of this study suggest that differences in utilization were influenced by clinical policies, the degree to which these policies were promoted, reimbursement, and the organization of radiology services.