Title: In-silico trials of targeted screening for abdominal aortic aneurysm using linked healthcare data: can the efficiency of the NHS Abdominal Aortic Aneurysm Screening Programme be improved whilst maintaining publicly acceptable levels of disease detection in an ethically acceptable manner
Funder: Department of Health and Social Care

Abstract: Background:_x000D_ _x000D_ An abdominal aortic aneurysm (AAA) is a swelling of the main blood vessel in the body, the aorta. If an AAA gets too large it can burst (rupture) and cause internal bleeding. This is usually fatal. If they are found before they burst, AAAs can be repaired by having an operation. To reduce the number of people dying from ruptured AAA the NHS offers AAA screening to men at the age of 65 (women rarely get AAA). About 280,000 men are invited for screening each year, with one in five men attending for screening. One in every 100 men screened are found to have an AAA. This screening programme costs the NHS about £7.75 million per year. Much of this cost is spent on screening the 99% of men who do not have AAAs. Some men who don't have an AAA also suffer unnecessary worry from the screening invitation and testing process._x000D_ _x000D_ Smoking is the main risk factor for AAA. As the number of people who smoke has decreased over time AAAs are becoming less common. In 2010, 1.50% of men screened by the NHS had an AAA and this fell to 0.97% in 2019. As AAAs become less frequent, AAA screening costs more per person found to have an AAA. Eventually the NHS will not be able to justify spending money on AAA screening. An alternative, more cost-effective approach is to only invite men for AAA screening if they are at high risk of having an AAA. This is done in the United States where only men who are current or ex-smokers are invited for AAA screening. This reduces the number of men who are screened. It is not known if this approach misses many men with AAAs in the group who are not offered screening however._x000D_ _x000D_ Research plan:_x000D_ _x000D_ In this research we will analyse results from the NHS AAA Screening Programme from 2013-2021. General practice records will be obtained for around one fifth of the men invited for screening using a process that ensures all men remain anonymous to the research team. By combining the results of AAA screening with general practice records we will work out what would have happened if only men with known risk factors for AAA had been invited for AAA screening. This work will be extended to see if there are other details in general practice records that can be used to identify men at high, or low risk of AAA. This information will be used to see if AAA screening can be targeted at groups of men who are at a high risk of having an AAA and, if so, whether such a targeted screening programme will still identify the majority of men with AAAs. The ethics and acceptability of targeted screening will be explored with members of the public._x000D_ _x000D_ Public involvement:_x000D_ _x000D_ This research has been planned with the public to find out what is important for those who might be affected by changes to the AAA screening programme. This identified that the main consideration in this research is to make sure that any targeted screening programme still diagnoses the majority of people with AAAs. During this research we will continue to consult with the public to ensure our work is relevant to those who will be affected by any recommendations resulting from this research._x000D_ _x000D_ Sharing our findings:_x000D_ _x000D_ The results of this research will be made available to the public and to researchers. We have good links with UK public health bodies that will ensure the results of this research are acted upon. _x000D_ _x000D_ Impact:_x000D_ _x000D_ This research will find out whether a new, more economic, way of delivering AAA screening programme can be designed that is acceptable to the public.

Lay abstract: Research question: Can the effectiveness of abdominal aortic aneurysm (AAA) screening be improved by targeting screening at individuals most likely to have an AAA, whilst ensuring that AAA detection rates remain acceptable to patients and the public?_x000D_ _x000D_ Background: Screening for AAA is both clinically and economically effective. The main determinant of this effectiveness is disease prevalence. AAA prevalence is decreasing over time, steadily reducing the efficiency of the current NHS AAA Screening Programme (NAAASP) screening policy. One alternative to whole population screening is targeted screening of high-risk groups such as smokers. Whether this would detect a clinically and publicly acceptable proportion of disease, and the extent to which it would improve cost-effectiveness is unknown._x000D_ _x000D_ Aim: To determine the clinical outcomes and cost-effectiveness of targeted AAA screening._x000D_ _x000D_ Objectives:_x000D_ _x000D_ 1) Explore the ethical implications and public acceptability of targeted AAA screening; _x000D_ 2) Link individual mens’ NAAASP screening records to primary care records and prepare the linked dataset for analysis;_x000D_ 3) Use the linked dataset to undertake in-silico trials of targeted AAA screening including long-term clinical and economic effectiveness modelling._x000D_ _x000D_ Methods: Rather than conduct an expensive and time consuming randomized trial to directly test targeted screening, we will undertake in-silico trials of targeted AAA screening. To determine success criteria for the in-silico trials, and as a specific research output, the ethics and issues around acceptability of targeted screening will first be explored using qualitative measures. To perform the in-silico trials individual mens’ outcomes from the NAAASP (2013 to 2021, ˜2,300,000 men, 1% with AAA) will be linked to primary care data from the Clinical Practice Research Datalink (CPRD) (20% overlap of records). Risk factors for AAA will be used as targeted screening criteria in in-silico trials, with diagnostic accuracy as the primary outcome. Trial results will be used to re-parameterise a discrete event simulation model of AAA screening to estimate the long-term (30 year) clinical and economic effectiveness of the targeted screening._x000D_ _x000D_ Timelines for delivery: Months 0-9: PPI group training, literature review, focus groups, qualitative data analyses and data cleaning/preparation. Months 10-18: PPI review of focus group work, targeted screening strategy development and in-silico trials. Months 19-30: Long-term clinical and cost-effectiveness modelling, PPI review of results, dissemination._x000D_ _x000D_ Anticipated impact and dissemination: We expect this project to have a direct and significant impact on NHS, UK and worldwide AAA screening policies. Our dissemination strategy will be to target those involved in screening policy decisions. The results of the research will be disseminated via our contact networks directly to Public Health England and the other UK AAA screening stakeholders, including an evidence review submission to the National Screening Committee. Conventional media will be used as the main route for public dissemination as this is the most effective way to reach those affected by this research. Academic audiences will be reached through peer-reviewed publications, conference presentations and online electronic dissemination.

Research activity codes: 4.4 POPULATION SCREENING;8.1 ORGANISATION AND DELIVERY OF SERVICES
Health categories: CARDIOVASCULAR