Screening for vascular disease promises major public health benefits, so long as it is not half-hearted

The Prime Minister has announced plans for a new programme in England to screen all men over 65 years of age for abdominal aortic aneurysm (AAA) and to assess adults for risk factors or early signs of heart disease, stroke, kidney disease and diabetes. Professor Peter Weissberg asks whether the proposals are realistic

Screening is a public health service that aims to identify people within a defined population that would benefit most from more tests, or treatment, to reduce the risk of a disease or its complications. Screening can involve offering people a test, taking body measurements or asking them questions. For these initiatives to work, they require access to a reliable diagnostic test and an effective treatment or other intervention.

The underlying premise behind the government’s announcement on AAA screening would appear to be sound. AAA causes 12,000 deaths per year in the UK, mostly because of rupture of an undiagnosed, asymptomatic AAA which could have been picked up with abdominal ultrasound and treated by surgical or endovascular repair. Atherosclerotic vascular disease – the predominant cause of heart attacks and strokes – is the major cause of premature death in the UK. It has a long asymptomatic gestation before it manifests as a frequently fatal vascular event. It occurs in people with recognisable and largely correctable risk factors. So, will the screening proposals make a public health difference? The answer to this is a possible yes, but only if the screening programmes and their consequences are properly resourced and managed.

Screening for AAA is the least contentious aspect of his proposals but a number of questions must be answered if the AAA screening programme is to be effective:

All men over 65 must be identified and undergo a competent ultrasound examination. It should be carried out within the patient’s community and by a trained ultrasonographer, which has implications for capital costs and appropriate skills training. Where will this money come from?

The programme will only be successful if it reduces the number of patients presenting acutely with ruptured aneurysms, which means most people at risk must be identified. Patients identified as at risk (AAA >5cm) will usually require further investigation by CT to determine their suitability for surgery or endovascular repair. Will the additional costs of investigation and intervention be forthcoming?

Not all AAA will be amenable to repair either for technical reasons or because of other conditions that would preclude safe intervention. The psychological and social implications (insurance, ability to drive etc) of knowing you have a ticking time bomb inside you are considerable. Will the NHS provide AAA support nurses or will GPs be left to pick up the pieces?

Screening for AAA will create an expanding cohort of patients who will require regular monitoring. These will be those who have been identified with aneurysms that are not yet at the size threshold for intervention. No medication currently exists to reduce the rate of AAA growth so these people will require regular ultrasound monitoring thereafter. And for those with a ‘clean sheet’ at 65 years, when will they be rescreened and at what age, if any, should screening cease?

And finally, but no less important, the UK National Screening Committee has examined the evidence and concluded that a screening programme for AAA would be cost effective for men over 65 years. There were insufficient data on which to base a similar conclusion for women and such evidence should be urgently sought to ensure they are not disadvantaged.

All of these issues are tractable but will require substantial resources. As always, the devil is in the detail.

Population screening - or more accurately ‘risk assessment’ - for risk factors for cardiovascular disease, diabetes and kidney disease is an altogether different prospect. The aim here is to identify risk factors or signs of very early disease-of which there are very few-in the hope that interventions will reduce the risk of the disease developing or progressing. Unlike AAA, where there is a simple binary diagnostic test-you either have it or you don’t-and a single intervention, cardiovascular risk prediction requires the integration of multiple factors to estimate a person’s risk and the application of multiple interventions, not all medical, to reduce it. Also, the greatest burden of disease resides in those sectors of the community that are least likely to respond to calls for risk assessment and are least willing or able to change their modifiable risk factors e.g. smoking, obesity, lack of exercise once identified. A risk assessment programme that favours the worried well and misses those at highest risk of the disease will only serve to increase inequalities in disease prevalence and health care provision.

Once level of risk has been estimated, there is the contentious issue of the affordable threshold for prescription of effective medications - strongly influenced by the cost of statins - currently set at a one in five chance of a major cardiovascular event over the next 10 years. With new anti-diabetes and anti-obesity drugs in the pipeline, there will be little respite in the economics debate despite the increasing availability of generic statins.

The BHF’s view is that all adults should have the opportunity to become aware of and understand their personal risk of developing cardiovascular disease so that they can take steps to reduce it if they wish. However, if the proposed risk assessment programme is to deliver genuine public health benefits, it must be supported by a whole raft of measures that enable people most at risk to modify their lifestyles and receive appropriate medication where necessary. This argues as much for social changes and a much more aggressive approach to the food and tobacco industries as it does for greater resources for the NHS to avert the huge potential burden of disease likely to be identified by mass risk assessment.

Professor Peter Weissberg is medical director at the British Heart Foundation