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A paper last year led to headlines that screening for aortic aneurysms does not reduce overall death rates. Not so, says Mr Shane MacSweeney, who argues that a national screening programme is long overdue
Not so, says Mr Shane MacSweeney, who argues that a national screening programme is long overdue
As a surgeon operating on a desperately sick patient with a ruptured aneurysm, often in the middle of the night, it is easy for me to see the potential benefits of aneurysm screening. While the advantages of preventing rupture are obvious, it is less certain whether the mortality and morbidity of performing prophylactic repair in an asymptomatic elderly population is justified.
AAA affects 7.6 per cent of men aged between 65 and 80. It is much less common (1.3 per cent) in women and presents at an older age. Ruptured AAA causes about 2 per cent of all deaths in men over 65. Risk factors for developing AAA include smoking, hypertension and raised LDL cholesterol. There is also a genetic element, making someone at greatly increased risk if a first-degree relative is affected.
Last year, the BMJ published a paper with the front-page headline 'Screening for aortic aneurysm does not reduce overall death rates'. This study does not invalidate the case for the national screening programme, which was recently given the green light in principle by the National Screening Committee.
Indeed the 2002 Multiple Aneurysm Screening Study tria · 2 has thrown up good evidence supporting screening, most notably the reduction of emergency workload for ruptured AAA by an impressive 70 per cent.
Chances of survival
Between 30-50 per cent of people with an AAA will die of rupture, knocking an average of nine years off their life.
The community mortality of ruptured AAA is about 85 per cent. Many will die before reaching hospital and of those who undergo surgery, mortality is 40-50 per cent. Preventing rupture is key.
This is mainly because aneurysms detected by screening are younger and so mortality rates for repair are lower than for those detected as incidental findings (approximately 3 per cent versus 9 per cent).
AAAs grow slowly at about 0.25cm/ year over many years. Risk of rupture is extremely low for small aneurysms, but increases with increasing size. This long 'latent period' lends itself to screening.
Ultrasound scanning is an ideal screening tool as it is 99 per cent accurate, safe and inexpensive (£20 per patient) and can be performed in the community. Some 95 per cent of aortas screened will be normal and not require a further scan. In Gloucester where screening has taken place since 1990, 86 per cent of men were happy to attend for a scan at the GP surgery at age 65.
Effects of a screening programme
Once a screening programme is established, the additional workload has been calculated as 2.1 extra elective AAA repairs per month in an average district general hospital with a 400,000 population. The proportion of AAA repairs performed as emergencies is expected to fall from 39 to 6 per cent over time. Since emergency repairs are very expensive and often disrupt the elective workload it is likely that existing resources could cope with the necessary surgery.
Good evidence for screening
In the Multicentre Aneurysm Screening Study (MASS) trial, 67,800 men aged 65-74 were invited to participate and divided into a screened and control group. At four years AAA-related mortality was 113 in the control group and 65 in the screened group, a reduction of 42 per cent (p < 0.0002),="" ie="" 53="" per="" cent="" of="" those="" who="" attended="" for="" a="">
The emergency workload for ruptured AAA fell by 70 per cent. There was no significant change in quality of life in the screened group. Screening also presented an opportunity for secondary prevention measures, such as smoking cessation.
Value for money
Although AAA screening fulfils the criteria for a screening programme it has to compete with other screening programmes for resources.
Cost-effectiveness analysis of the MASS tria · 3, based on a screening cost of £20 and elective repair at £6,909 against emergency repair cost at £11,176, showed that after four years the screened group cost £98.42 each and the control group £35.03, giving a cost per QALY of £28,389.
This will continue to improve over time as further deaths from rupture are prevented giving an estimated cost per QALY of £10,000 at 10 years. NICE uses a figure of £30,000 per QALY as a benchmark for assessing acceptable cost.
What GPs can do
AAA screening is clinically effective, and cost-effective. The extra workload could be managed without adversely affecting other provision.
As GPs are increasingly involved in funding decisions, please look favourably on this one. And if no national screening programme is forthcoming, I would encourage GPs to set up a local one. In the meantime, if you suspect or discover an AAA get it scanned and referred. You may also wish to arrange scans in first-degree relatives of people with AAA.
Shane MacSweeney is consultant vascular surgeon, Queens Medical Centre, Nottingham; vascular tutor Vascular Society of Great Britain and Ireland and Royal College of Surgeons of England
Criteria for a screening programme (Wilson-Junger)
·The condition should be an important health problem
·There should be accepted treatment
·There must be facilities for treatment
·There must be a latent (or very early) stage when early detection confers an advantage
·The screening test must be acceptable to the public
·Must understand the natural history of the disease
·Policy on whom to treat
·Balance costs against medical care as a whole
·Continuing case-finding process
Australian paper on AAA screening1
In November last year the BMJ published a paper from Western Australia by Norman et al on screening.
The study looked at men aged 65-83 identified from the electoral register. No attempt was made to exclude those unlikely to benefit or to attend screening, for example those with major co-morbidity or advanced malignant disease.
The study was analysed by intention to treat. More than 50 per cent of those aged over 75 did not attend for screening and
two-thirds of the aneurysm-related deaths occurred in this group.
The authors themselves said that 'the chief reason for our overall result seems to be our failure to identify and exclude men who were unlikely to attend'. They also stated in correspondence (see http://bmj.bmjjournals.com/cgi/eletters/329/7477/1259#88494) 'the MASS trial indicates that screening should be introduced in the UK our results should not undermine this'.
This study does not invalidate the argument for a screening programme but does emphasise that screening programmes must be carefully designed and targeted if they are to be effective.
1 Population-based randomised controlled trial on impact of screening on mortality from ruptured abdominal aortic aneurysm. PE Norman, et al.
2 The Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Ashton HA et al. Multicentre Aneurysm Screening Study Group.
Lancet. 2002 Nov 16;360(9345):1531-9
3 Multicentre aneurysm screening study (MASS): cost-effectiveness analysis of screening for abdominal aortic aneurysms based on four-year results from randomised controlled trial. Multicentre Aneurysm Screening Study Group.
BMJ. 2002 Nov 16;325(7373):1135