Estimating overdiagnosis in screening for abdominal aortic aneurysm: could a change in smoking habits and lowered aortic diameter tip the balance of screening towards harm?

Summary box

• Clinical context—Abdominal aortic aneurysms (AAAs) are often asymptomatic until they rupture, when the death rate is greater than 80%. If diagnosed before rupture, AAA can be treated with surgery, which has a mortality of 4-5%

• Diagnostic change— Sweden, the UK, and the US have initiated screening programmes for AAA. There are also proposals to change the aortic diameter for diagnosis from ≥30 mm to 25 mm

• Rationale for change—Early diagnosis by screening allows the opportunity of surgery to prevent ruptures

• Leap of faith—Detecting asymptomatic aneurysms will reduce AAA mortality and morbidity

• Impact on prevalence—Our estimates indicate that screening almost doubles AAA prevalence, but most AAAs are small and at low risk of rupture. Changing the definition of an AAA from 30 mm to 25 mm would double prevalence again

• Evidence of overdiagnosis—We estimate that if 10 000 men are invited to screening, 46 AAA deaths can be prevented over 13-15 years but 176 would have an AAA ≥30 mm detected that remained asymptomatic after 13 years. A recent drop in AAA prevalence reduces the benefits of screening and worsens the benefit:harm ratio

• Harms of overdiagnosis—Asymptomatic men are labelled at risk of a life threatening condition for which they will be under lifelong surveillance. Of 10 000 men invited to AAA screening, 37 (95% confidence interval 15 to 60) overdiagnosed men had unnecessary preventive surgery, of whom 1.6 (1.4 to 1.7) died

• Limitations—Figures for exact calculations of overdiagnosis are not available and unlikely to emerge. The psychosocial consequences of living with a screen detected AAA are inadequately investigated. Cost effectiveness data on screening are inconclusive

• Conclusion— Screening programmes have changed the meaning of an AAA diagnosis from a life threatening condition to a risk factor. AAA screening programmes should be …