Scottish experience of double reading in the National Breast Screening Programme

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The aim of this study was to assess and quantify the results of the double reading regime in the Scottish Breast Screening Programme for the years 1992–1996, and to use this information to make a recommendation as to whether this practice should be continued. This study is a retrospective data analysis of the Scottish Breast Screening Programme (part of the UK NHSBSP). Outcome data were analysed for all women attending the Scottish Breast Screening Programme from 1 April 1992 to 31 March 1996. The number of additional cancers detected by the second reader only and the number of additional women recalled by the second reader only were assessed. Double reading resulted in the detection of 259 additional cancers by the second reader in the 4-year period. This represents 10.5% of the total cancers detected in that time. The effect of double reading on the number of recalls can only be obtained for a subset of the data. Analysis of this subset showed that an additional 4616 women (27% of the total number of women recalled) were recalled to obtain 170 additional cancers (12% of total cancers). Double reading has increased the cancer detection rate of the Scottish Breast Screening Programme. Over 10% of cancers were detected only by the second reader. This improvement in sensitivity has been maintained over the 4 years reviewed. Using a second reader resulted in a 13% increase in the cancer detection rate, although this was associated with a 37% increase in recall rate. At present we find no reason to discontinue the practice of double reading, although this will be reviewed at intervals as technological advances are introduced.