Cardiovascular screening to reduce the burden from cardiovascular disease: microsimulation study to quantify policy options

Sir,

The authors have attempted to generate evidence that helps resolve the controversy surrounding screening programs. Although they have limited their investigation to cardiovascular diseases, there are several issues that affect other diseases as well.

The primary question they have attempted to answer is whether universal screening to identify high risk individuals is preferable to population-wide interventions aimed at reducing population risk. In the case of cardiovascular diseases (notwithstanding the narrow definition used in the study) in the UK, the evidence favours population-wide interventions over universal screening.

If the outcome measure is 'averted mortality', the choice is straightforward. However, often the decision to implement one or other screening method is far more complex.

Decision makers are constrained by the available resources (manpower, budgetary allocation, time available, etc.), evidence pool (number and quality of studies, whether the evidence provides insights/ solutions for the problem, whether the evidence is generalizable to the target population, etc.), target population (size, structure, behavioural characteristics, level of engagement with the healthcare system and other functionaries, presence of social security, etc.), and considerations related to implementation, monitoring and evaluation, among other factors.

Further, there are questions related to the disease(s)- is there enough knowledge about the natural history, aetiology, risk factors, etc. to justify large-scale implementation of a screening program? Is the disease/ condition of sufficient importance (high prevalence; high morbidity and/or mortality rates)? Is the disease/ condition associated with/ a risk factor for other diseases/ conditions?

In addition, careful consideration of the screening test (validity-sensitivity, specificity, predictive accuracy; cost; cost-effectiveness; requirements for administration of the test; acceptability of the screening test by experts and practitioners, etc.), and subsequent intervention(s) (evidence supporting the intervention(s); scalability of the intervention(s); manpower and logistics required for implementation of the intervention(s), etc.) is also required.

It is quite possible that universal screening may be suitable in one context, but unsuitable in another- what works for cardiovascular diseases may not work for cancers.

However, the mere institution of universal screening without simultaneously initiating population-wide interventions to lower risk will simply result in (potentially) improved detection rates in the face of unaltered risk profiles. From a common sense and public health perspective, this is not desirable. The objective should always be the improvement of health, while simultaneously improving detection rates through screening measures. Instituting population-wide interventions while conducting high-risk screening is a logical way to achieve the same.

Universal screening is wasteful, and is unlikely to alter risk levels. High risk screening requires the identification of those at high risk before screening them- the approach adopted by the NHS- and will also have no impact on disease incidence rates (the rate of occurrance of new disease, as against the detection of new cases). However, the case detection rate may increase, reflecting better detection rather than anything else. This will also result in an increase in disease prevalence.

Population-wide interventions are attractive as small individual level improvements can translate to large population-level benefits. Of course, the implementation of such interventions may be patchy, and benefits may not be of the magnitude anticipated. However, any reduction in risk is preferable to the maintenance of the status quo.

The opportunity for disease prevention that screening provides must be exploited through careful and judicious use of available resources. The challenge lies in determining the best approach to maximize gains at an affordable cost.