Objective: Estimates of adherence to mammography screening guidelines vary, in part, due to lack of consensus on defining adherence. This study estimated adherence to repeat (two successive on-time screenings) and regular screening (three or more successive screenings) and evaluated the impact of varying operational definitions and evaluation periods.
Methods: The study included women aged 50-80 without a history of breast cancer who: were on a biennial screening cycle and due for a screening mammogram between 1995 and 1996; underwent screening (index date) in response to a reminder letter; and belonged to Group Health, an integrated health care delivery system in Washington State, for 6 or more years after the index date. Automated records provided information on enrollment, health care utilization, and procedures.
Results: Among 1336 women, 67-82% experienced a repeat screen. Adherence to regular screening over the 6-year evaluation period was 42-84%--and higher with longer allowable intervals between screenings, when definitions did not require on-schedule screenings, when intervals were reset after a diagnostic mammogram, and for shorter evaluation periods.
Conclusion: Estimates of adherence to screening guidelines varied by the operational definition of "success" and time period of evaluation. Consensus in definitions and terminology is needed to compare evaluations.