A Study of the Safety of Targeted AAA Screening

This study is a data linkage project within which we aim to model the impact on the NHS AAA Screening programme of a targeted approach to screening by targeting men who smoke. This in-silico study will generate a hypothetical population based on primary care datasets with known outcomes from screening (we know which men have an aneurysm and who do not) to determine the feasibility and safety of this approach.

An abdominal aortic aneurysm (AAA) is present in 5-10% of men aged between 65 and 79 years and may be defined as an abdominal aortic diameter 3cm or above. In 2013 the NHS AAA screening programme (NAAASP) was fully rolled out across England with the aim of reducing AAA mortality in men aged 65 and over, based on evidence that screening reduces AAA-related mortality, and is highly cost effective. Within NAAASP, men with a large AAA (≤5.5cm) are referred for consideration of surgery whilst men with small AAA (≥5.4cm) are referred into surveillance (3.0-4.4cm: 1 year surveillance, 4.5-5.4cm: 3 months surveillance) as per standard operating procedures. In England 284,583 men were offered ultrasound screening (2015-2016), however, the number of men identified with AAA was 2,549 at a cost of approximately £7,755,000. This highlights one of the main problems with AAA screening in that the majority of men screened do not have disease. This also brought the number of men within AAA surveillance to 13,1047 whom do not require early surgery. Several studies have investigated quality of life (QoL) in those who are screened for AAA, with one reporting short-term decreases in QoL at 1 year and four demonstrating no clinically important decrease in QoL in those screened positive compared with an unscreened control group. This has raised the issue of harms versus benefit however, AAA screening is not the same worldwide. For example, within The U.S. Preventive Services Task Force AAA Screening is recommended only for men aged 65-75 who have ever smoked as this group "stands to benefit the most from early detection and reparative surgical treatment due to a relatively higher prevalence of larger AAAs" . The screening programme described thus deemed men who have never smoked as lower risk for AAA and lower risk for rupture yet in England, we screen every man at the age of 65. Although several risk factors for AAA have been identified, smoking is the only modifiable risk factor that has been associated with the development, expansion and rupture of AAA with a causative link revealed in vivo within a mouse model. Population based studies have also demonstrated that smoking prevalence over time is linked to changes in AAA mortality. It is possible that screening based on a history of smoking is feasible and safe, however, no evidence exists that this would be the case. In England details for men eligible for AAA screening is identified based on primary care data in that men registered with a General Practitioner (GP) who are 65 within that year are invited to screening. Primary care data may also be able to identify men with a history of smoking and other known risk factors for AAA including hypertension, heart disease and stroke.