Abnormal call rate
Why is this important? This is an important indicator in assessing the performance and quality of mammogram imaging and its interpretation, thus informing whether additional testing and diagnostic follow-up procedures are required for screening participants.
A very high abnormal call rate may indicate an increase in false-positive rates and, consequently, an increase in unnecessary follow-up tests and stress on patients. Conversely, a very low abnormal call rate may result in lower cancer detection rates. Generally, abnormal call rates for initial screens tend to be higher than subsequent screens. With the support of the Partnership, the breast cancer screening community has developed a framework to help optimize abnormal call rates across the country.
Indicator definition: The percentage of screening mammograms that were identified as abnormal and therefore required additional testing and follow-up.
Target:
- Initial screens: <10%
- Subsequent screens: <5%
Measurement timeframe:
- January 1, 2019 to December 31, 2019
- January 1, 2020 to December 31, 2020
Indicator calculation:
- Numerator: The number of screening mammograms identified as abnormal.
- Denominator: The total number of screening mammograms in the measurement timeframe.
Additional considerations: Abnormal call rate is most informative when interpreted in the context of positive predictive value (PPV), cancer detection rate (CDR), cancer incidence rate, and post-screen cancer rate. This indicator can be impacted by several factors such as the screening interval, radiologists experience and reading volumes, mammographic features, screening technology and population characteristics like breast density and age.
Abnormal call rate among individuals aged 50-74, who were screened within a screening mammography program, by jurisdiction – 2019 and 2020
Data table and footnotes
The abnormal call rate (combined for initial and subsequent screens) varied by jurisdiction across the country. Within individual jurisdictions, the abnormal call rate remained relatively stable from 2019 to 2020, with the exception of Northwest Territories. The abnormal call rate in Northwest Territories decreased from 7.3% in 2019 to 4.9% in 2020.
Abnormal call rate among individuals aged 50-74, who were screened within a screening mammography program, by jurisdiction and age group – 2019 and 2020
Data table and footnotes
The abnormal call rate mostly decreased by age. No significant variation was observed in the abnormal call rate between 2019 and 2020 in most jurisdictions. The 50-59 age group had the highest abnormal call rate in most jurisdictions, with rates ranging from 5.7% to 10.3% in 2019 and 5.0% to 11.0% in 2020. The lower abnormal call rate observed in those above 60 years in most jurisdictions could be attributed to the fact that older women are more likely to have an extensive screening history for comparison by radiologists and less dense breast tissue, thus improving interpretation of results.
Abnormal call rate among individuals aged 50-74, who were screened within a screening mammography program, by jurisdiction and screening sequence — 2019 and 2020
Data table and footnotes
In both 2019 and 2020, abnormal call rates for initial screens were higher than subsequent screens in all jurisdictions. Rates for initial screens ranged from 11.3% to 22.8% in 2019 and 11.6% to 21.9% in 2020.
British Columbia, Saskatchewan, Manitoba, Ontario, Quebec, Nova Scotia, and Newfoundland and Labrador were unable to break down the subsequent screens by the specified months; all the subsequent screens were combined for these seven provinces. The 2019 abnormal call rates for subsequent screens in these seven jurisdictions ranged from 3.5% in Manitoba to 8.8% in Quebec. In provinces with specific month intervals for subsequent screens i.e. Alberta, New Brunswick and Prince Edward Island, the rates for subsequent screens were relatively consistent across screening intervals within each jurisdiction.