Screening mammography: experience in a health maintenance organization

To evaluate (a) the relationship between mammogram interpretation and diagnosis of new breast cancer and (b) interprovider variation in mammogram interpretation.

Interpretations of screening mammograms (133,668 mammograms in 114,899 women) acquired during 21 months in a large health maintenance organization were categorized (categories 1-5) with use of a standard format. During 1 year after mammography, new breast cancer was identified with use of claims data. Interprovider variation in the categories read was evaluated, and percentages of these categories were correlated with breast cancer detection.

Over the 21 months, 1,018 mammograms were followed by a diagnosis of new breast cancer. The category of mammogram interpretation was strongly associated with the diagnosis of new breast cancer; in 47.5% cases of category 5 mammograms, breast cancer was diagnosed. There was substantial interprovider variation in the percentages of category 3, 4, or 5 mammograms read. The percentage of category 4 and 5 mammograms read correlated inversely with the likelihood of cancer detection (Pearson correlation coefficient [r] = -.4778 after log-log transformation, P < .001).

A strong correlation existed between a mammographic abnormality suggestive of cancer and its detection; however, substantial interprovider variation in the reading of category 3, 4, and 5 mammograms and their positive predictive values existed. Reduction of interprovider variation should improve quality of care because the number of false-negative and false-positive mammograms should decrease.