Slippage in the NHS breast screening programme: an assessment of whether a three year screening round is being achieved

Background-The NHS breast screening programme (NHSBSP) was established in 1987 to screen women aged 50-64 every three years to achieve a significant reduction in breast cancer mortality. Ensuring that women are re-invited every three years (that is, a three year screening round is in operation) is becoming increasingly difficult as pressure on the service rises. Coverage measures the proportion of eligible women receiving a screen in the previous three years and is currently used as an NHS performance indicator, while uptake measures the proportion of invited women who attend for screening. Data for 1996/1997 for the the Test Midlands NHSBSP show that, although uptake among 50-64 year olds was in excess of the 70% target at 78%, coverage was 10% below this at 68%. The discrepancy between coverage and uptake is likely to in part reflect "round slippage" in which women are re-invited at three years or more from their previous screen. To investigate the extent to which slippage is occurring in the region a technique for assessing round length independently of coverage was developed. Methods-Records for women receiving routine recall (incident) screens between 1994 and 1997 in the West Midlands NHSBSP were examined and the time between the most recent screen and the previous screen measured in months. Findings-Of 73 785 women screened in 1996/1997, 46.3% had a round length of under three years, although 74.9% had been re-screened within 38 months of the previous screen. Overall the regional programme was estimated to have a round slippage of approximately two months. Conclusions The West Midlands NHSBSP operates to high standards in terms of uptake and cancer detection, but round slippage must be reduced. The lack of quantitative data with which to assess round length has hindered assessment in the past. The simple technique developed in this study will allow assessment of round length to be used routinely as the key quality assurance measure for the programme.