Screening: policy context
The Scottish Government follows the advice of the UK National Screening Committee. This is an expert committee that advises ministers and the NHS in the four UK countries about all aspects of population screening and supports implementation of screening programmes. It considers all aspects of screening including the case for introducing new population screening programmes and for continuing, modifying or withdrawing existing population programmes against a set of internationally recognised criteria (see Introduction). This includes assessing the points under 'Factors to consider about screening' below.
The Scottish Government has recently established a Scottish Screening Committee, which will fully consider the implementation of all UK National Screening Committee recommendations in the context of the specific Scottish circumstances.
Several policy documents on general cancer policy include screening as part of the initiatives (e.g. see Breast cancer: policy context web page).
Why is screening different to other health services?
Screening differs to other aspects of the health service as it targets and offers apparently healthy people help to make better informed choices about their health. There are, however, risks involved in screening. See Public Health England’s Guidance, NHS population screening explained.
Screening can reduce the risk of developing a condition or complications but it cannot offer a guarantee of total protection from a particular illness. In any screening programme, there can be false positive results (wrongly reported as having the condition) and false negative results (wrongly reported as not having the condition). There are therefore opportunity costs and harms surrounding screening. For this reason, the ethical, economic, legal and social consequences should always be carefully considered prior to the introduction of a new screening programme (see HealthKnowledge). In the UK these aspects are largely overseen by the UK National Screening Committee, which considers evidence on benefits, harm and risks before recommending that the NHS develops a particular screening programme, and is increasingly presenting screening as risk reduction to emphasise this point.
Factors to consider about screening
While screening programmes can bring benefits they can also have some risks. As part of the criteria noted in the Introduction under ‘When is screening appropriate?’ the following are considered by the UK National Screening Committee before a screening programme is implemented:
- False negatives – provide false reassurance and can mean that some individuals may not seek medical advice when they should.
- False positives – result in anxiety and further invasive diagnostic tests or treatment which risk side effects and carry economic cost.
- Overdiagnosis - for example, the detection of non-lethal lesions that meet the histologic criteria for cancer or cancer precursors and will lead to unnecessary treatment. A special collection issue of the British Medical Journal (4th March 2015) (accessible via Athens or the NHS Knowledge Network) focused on the issue of overdiagnosis, including that resulting from screening (papers by Johansson et al. (2015), Van den Bruel et al (2015)., and Baratt (2015)).
- Harm of the screening test, including inconvenience and potential psychological harm.
- Epidemiological artefact - may increase the perceived benefits of the screening programme due to:
- Lead Time Bias: screening appears to increase survival time simply because the disease is detected earlier. Once controlled for, there may be little or no positive impact of the screening test as the total survival time can be the same with or without screening.
- Length Time Bias: An overestimation of survival because long-duration cases are more likely to be detected and treated than short-duration, and more dangerous, conditions.
- Detection rate (i.e. the proportion of the total referred for diagnosis which turn out to be actual cases) – if this is reduced by the introduction of a screening programme, i.e. if more people need to be screened to identify one case, this will create pressure on health systems. For a good example see Weatherhead and Lawrence’s (2006) analysis of the impact of the creation of open access melanoma screening clinics where detection rates subsequently reduced.
Only when a screening programme is assessed as having potential to do more good than harm at the population level will it be advocated and policy recommendations made by the UK committee. Best practice for the introduction of screening programmes has been described (Gray et al., 2008), but assessing the long-term impacts can be challenging and the impacts of screening on mortality have been found to be equivocal (Saquib et al., 2015, Prasad et al., 2016).
The implementation of health improvement programmes which seek to identify individuals at high risk of premature death (e.g. from cardiovascular disease) but which have not been introduced under the auspices of the National Screening Committee means that the associated effectiveness and risks may not been assessed in relation to the screening criteria.
Genetic screening is distinct from screening for other conditions and has other associated issues. It has the potential to impact not just on the individuals being screened, but also their family members and society generally, which raises a number of ethical issues (see HealthKnowledge): consent to being screened; counselling; the risk of stigma; and disclosure to family members.