Screening for abdominal aortic aneurysm: should we lower the intervention cut-off point?BMJ 2012; 344 doi: http://dx.doi.org/10.1136/bmj.e3111 (Published 04 May 2012) Cite this as: BMJ 2012;344:e3111
- Anne Andermann, assistant professor
- 1Department of Family Medicine, Faculty of Medicine, McGill University, Montréal, QC, Canada, H3T 1M5
In accordance with the recommendations of the US Preventive Services Task Force and the UK National Screening Committee in favour of screening for abdominal aortic aneurysms (AAAs),1 2 the United Kingdom’s NHS began phased implementation of routine screening for all men at age 65 years. According to the guidelines,3 about five in every 1000 men screened will have an AAA greater than 55 mm and will be referred for surgery to prevent rupture and related death. In addition, another 35 men will have an AAA of 30-54 mm and will be followed with regular ultrasounds, lifestyle counselling, and medical management. The remaining 960 of 1000 men with an aorta less than 30 mm will be discharged from the programme with no further follow-up. However, in the linked study (doi:10.1136/bmj.e2958), Duncan and colleagues present new evidence showing that men with a slightly enlarged aorta (25-29 mm) are also at increased risk of death and hospital admission as a result of chronic disease.4 These results beg the question—should the cut-off point for a “normal” screening test be lowered to 25 mm or should we retain the current cut-off point of 30 mm?
Making screening policy decisions is a complex undertaking that has evolved over the past 40 years, with an increasing emphasis on results based management, evidence based medicine, and patient choice.5 The difficulty in establishing screening cut-off points is that risk exists on a continuum and does not increase in a stepwise manner. In the United States there has been great controversy over whether to start breast cancer screening at age 40 or 50 years, and more recently some experts have argued that women are being over-screened and that the harms outweigh the benefits for the great majority.6
When determining cut-offs points it is important to ask “what is the added benefit to the person being screened?” Are those with an aortic diameter of 25-29 mm really at higher risk of morbidity and mortality? Are there interventions that can reduce morbidity and mortality in this group? Do the potential benefits outweigh the harms? What are the opportunity costs?
In Duncan and colleagues’ study, out of 8146 men screened, there were 2.2% aneurysm related deaths in men with an aortic diameter greater than 30 mm (9/414) versus only 0.1% in the 25-29 mm group (1/669) and 0.01% in the under 25 mm group (1/7063). Similarly, there were 63.5% aneurysm related hospital admissions in the over 30 mm group (263/414) versus only 4.5% in the 25-29 mm group (30/669) and 0.6% in the less than 25 mm group (44/7063). Because screening for AAA does not affect overall mortality, but only aneurysm related mortality,7 and because the repair of small aneurysms provides no added benefit,8 the number needed to screen to benefit one person in the 25-29 mm group would be much higher than in the over 30 mm group. In addition, all screening is associated with inherent harms. An estimated one in 20 men dies during elective surgical repair of an aortic aneurysm. This may be acceptable for men at very high risk of aneurysm rupture and related death, but for men at lower risk the harms of screening and ongoing follow-up may outweigh the benefits, so greater caution is needed.
Indeed, the current study shows no overall difference in mortality between the less than 25 mm group and the 25-29 mm group after adjusting for known cardiovascular risk factors. Changing the cut-off point for intervention is therefore unlikely to have an effect on overall mortality. Even if the 25-29 mm group has somewhat increased rates of hospital admission for cardiovascular disease, diabetes, and chronic obstructive pulmonary disease, screening for AAA is not the most effective means of reducing this increased risk. It has long been known from autopsy studies that fatty streaks begin to appear in the aorta in adolescence or even in childhood, particularly among people with risk factors such as smoking, impaired glucose tolerance, and obesity.9 Prevention of chronic disease therefore needs to be integrated,10 and it needs to start earlier. Efforts aimed at reducing risk factors in the entire population are likely to have a greater effect than focusing on lifestyle counselling for the relatively small proportion of older men with an aortic diameter greater than 25 mm. Screening (which is a form of secondary prevention) is part of a wider continuum of strategies for improving population health that ranges from health promotion and disease prevention to treatment and rehabilitation (fig 1⇓). The best approach is to prevent disease before it occurs by tackling the underlying social causes of poor health.11 Too often we blame the individual for making unhealthy choices and spend money on costly hospital based interventions, when really we need to change the social and physical environment to “make the healthy choices the easy choices.”12
Cite this as: BMJ 2012;344:e3111
Competing interests: The author has completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declares: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.
Provenance and peer review: Commissioned; not externally peer reviewed.