Safety of Men with Small and Medium Abdominal Aortic Aneurysms Under Surveillance in the National Health Service Screening Programme.

BACKGROUND: Population screening for abdominal aortic aneurysm (AAA) has commenced in several countries, and has been shown to reduce AAA-related mortality by up to 50%. Most men who screen positive have an AAA below 5.5cm in diameter, the referral threshold for treatment, and are entered into an ultrasound surveillance programme. This study aimed to determine the risk of ruptured AAA (rAAA) in men under surveillance. METHODS: Men in the NHS AAA Screening Programme who initially had a small (3-4.4cm) or medium (4.5-5.4cm) AAA were followed-up. The screening programme's database collected data on ultrasound AAA diameter measurements and dates of referral and loss to follow-up. Local screening programmes recorded adverse outcomes, including rAAA and death. Rupture and mortality rates were calculated by initial and final known AAA diameter. RESULTS: A total of 18,652 men were included (50,103 men years of surveillance). Thirty-one men had rAAA in surveillance, of whom 29 died. Some 952 men died from other causes during surveillance, mainly cardiovascular complications (26.3%) and cancer (31.2%). The overall mortality rate was 1.96% per annum, similar for men with small and medium AAA. The rAAA risk was 0.03% per annum (95% confidence interval 0.02-0.05%) for men with small AAA, and 0.28% (0.17-0.44%) for medium AAA. The rAAA risk for men with AAA just below the referral threshold (5.0 to 5.4 cm) was 0.40% (0.22-0.73%). CONCLUSIONS: The risk of rAAA in surveillance is below 0.5% per annum, even just below the present referral threshold of 5.5cm and only 0.4% of men in surveillance are estimated to rupture before referral. It can be concluded that men with small and medium screen-detected AAA are safe provided they are enrolled in an intensive surveillance program, and that there is no evidence that the current referral threshold of 5.5cm should be changed.