Guidance

UK NSC: evidence review process

Updated 19 February 2024

1. Overview

This publication describes how the UK National Screening Committee (UK NSC) reviews evidence relating to proposals to introduce, modify or cease screening programmes.

The UK NSC makes evidence-based recommendations to ministers so that thousands of people can be helped by health screening programmes every year.

The UK NSC makes recommendations relating to 2 types of screening programme: population screening and targeted screening. The committee also considers stratified screening. These are distinct from routine clinical care in which a person with health concerns or symptoms may be offered tests by a clinician to assess their risk of disease.

1.1 Definitions

Population screening programme

A nationally delivered, proactive (individuals are actively invited for screening) screening programme which aims to improve health outcomes in people with the condition being screened for, and/or offer information to enable informed choices. It is offered to a group of people identified from the whole population, and defined demographically such as by age or sex.

Targeted screening programme

A nationally delivered proactive screening programme which aims to improve health outcomes in people with the condition being screened for, among groups of people identified as being at elevated/above average risk of a specific condition. Compared to the general population, the target population may be at higher risk because of lifestyle factors, genetic variants or having another health condition.

Targeted screening differs from population screening as it aims to identify groups of people with a higher risk of a specific condition beyond demographics such as age or sex. For example, individuals who smoke are at a higher risk of developing lung cancer regardless of their age and sex.

Stratified screening programme

A nationally delivered, proactive screening programme, offering testing which varies in frequency and modality (varying types of test offered), according to the level of individual risk. This is designed to achieve a more favourable balance of benefits and harms at individual as well as population level.

Stratified screening can be used to complement both targeted and population screening programmes. For example, people with a family history of breast cancer can be referred to a high risk clinic and screened more often depending on their level of risk.

2. UK NSC remit

Screening is a public health service. The purpose of a screening programme is to offer a test to members of a defined population who do not necessarily perceive that they are at risk of, or are already affected by, a disease or its complications. The test is to identify those individuals who are more likely to be helped than harmed by further tests or treatment to reduce the risk of disease or its complications.

Potential screening programmes that are within the UK NSC’s remit are considered on a case by case basis. The following characteristics are a guide to what is in scope under that remit:

1. The target population to be screened should be large enough to enable safe, clinically and cost effective screening.

2. The cohort to be offered screening would regard themselves as not necessarily having symptoms of the disease. In other words, the business of the committee should be apparently healthy people.

3. There should be an effective means of identifying, contacting and keeping a list of the whole cohort to be offered screening.

4. The population should be proactively approached and offered screening. They should be properly informed of the potential benefits and risks in order to help them make an informed choice.

5. The primary purpose of screening should be to offer benefit to the person being screened. If there is no possibility of benefit to the person being offered screening then it should no longer be considered as a potential screening programme.

The UK NSC assesses evidence for screening against its criteria for appraising the viability, effectiveness and appropriateness of a screening programme. These cover important issues relating to the condition, the test, the treatment and the effectiveness of a screening programme. The criteria provide the framework for reviewing the evidence for screening for a broad range of conditions.

The updated criteria include targeted as well as population screening in line with the 2022 launch of the committee’s revised terms of reference and expanded remit.

The UK NSC has made recommendations on whether or not to introduce screening programmes for more than 100 conditions. The recommendations divide into 2 broad types:

1. Conditions for which population screening programmes are not recommended.

2. Conditions for which population screening programmes are currently recommended.

The evidence informing these recommendations is updated on a regular basis.

If significant evidence is published in between regular reviews, the UK NSC can consider evidence for an early topic update.

The committee also reviews evidence for suggested changes to existing screening programmes (major modifications) and suggestions for new topics that it has not previously considered. See UK NSC annual call: submitting a screening proposal.

3. Principles

Horizon scanning principles underpin the UK NSC evidence review process.

Horizon scanning is the ‘systematic examination of information sources to detect early signs of important developments’ ^{[footnote 1]}. It typically consists of the following steps:

• identification of developments of potential interest

• filtration, in which developments are triaged to establish what is their evidence base and what is their relevance

• prioritisation of the most important relevant developments into an organisation’s objectives using more refined criteria

• assessment, in which developments are analysed more closely

• dissemination of the outputs of assessment to stakeholders

• follow-up, in which developments are integrated into the organisation’s work

The UK NSC evidence review process incorporates:

• regular, scheduled reviews of existing recommendations

• proactive searching of sources for new developments in research, international policy making and emerging technologies

• opportunities for internal and external stakeholders to draw the UK NSC’s attention to developments

• consultation and engagement with stakeholders

The UK NSC stakeholder engagement strategy sets out how the committee aims to involve stakeholders at all appropriate stages of the evidence review process.

The UK NSC conducts regular reviews on the evidence for screening where there is an existing recommendation:

• not to offer population screening

• to offer population screening

It also reviews evidence for screening:

• when new evidence is published which brings into question a current recommendation

• when a proposal is made to modify, or make big changes to, a current screening programme

• when a new topic (condition or technology) which has not been previously reviewed by the UK NSC is identified – see UK NSC annual call: submitting a screening proposal

• when the National Institute for Health and Care Excellence (NICE) or the Scottish Intercollegiate Guidelines Network (SIGN) suggest that an existing targeted screening guideline should be delivered through a nationally managed targeted screening programme

4. Products

4.1 Evidence maps

UK NSC evidence maps are rapid evidence products. They provide an evaluation of the ‘volume and type’ of evidence on a single question or set of questions on a given screening topic.

They have an important function within the evidence review process. Evidence maps have 3 main purposes, which are to:

• gauge if there have been significant developments in the evidence base on important questions identified in previous reviews of the topic

• establish if a current recommendation can be reaffirmed without additional work when there has been little, or no, change in the evidence base

• establish if a topic should be prioritised and / or is likely to benefit from further assessment through the development of different types of evidence product, for example evidence summaries (rapid reviews), systematic reviews, cost effectiveness studies, disease modelling exercises or primary research

Evidence maps provide a consistent first filtration step in the UK NSC evidence review process. In 2022, they formally replaced evidence summaries as the first step in reviewing existing recommendations not to offer screening. For many of these topics it had become clear there was not enough new evidence to justify conducting a new evidence summary every 3 years. Evidence maps are an effective way of allowing the committee to keep on top of developments while focusing on more detailed evidence work where there is significant new evidence.

Evidence maps are used to review evidence for new and existing topics from all possible peer-reviewed published sources. They help make sure the committee’s recommendations reflect the most up to date high quality evidence, enable the UK NSC to filter out topics with poorer evidence bases and to identify gaps in evidence which might need more research.

As filtration products, they focus attention on whether further assessment work on a topic is justified using a more substantial evidence product.

4.2 Evidence summaries

Evidence summaries gauge the volume, type and direction of the evidence on a single question or set of questions on a given topic. They are sometimes called rapid reviews but are not systematic reviews produced quickly. Their purpose is to:

• gauge if there have been significant developments in the evidence base on important questions identified in previous reviews on the same topic

• establish if a current recommendation can be reaffirmed

• establish if a topic is likely to benefit from further assessment through the development of different types of evidence product, for example a systematic review, cost effectiveness study, disease modelling exercise or primary research

UK NSC evidence summaries build on the level of detail provided by evidence maps by including a discussion (synthesis) of the included evidence, an appraisal of its quality and applicability, and whether the criteria it seeks to address are met or not. As with evidence maps, a question-led approach is used. For consistency, the UK NSC has developed a checklist to ensure all necessary elements are included in the final report.

The aim of an evidence summary is to provide a balanced discussion of the evidence that does not overly rely on one study or set of studies. Four components should be considered, and these should inform the reviewer’s judgement on whether criteria are met, not met or uncertain. These components are well established and are:

• quantity – this could include discussion of the number of studies, number of subjects in relation to particular outcomes, range of effects, sample size or power

• quality – checklists provide a structured means of assessing the quality, or risk of bias, of individual studies and typically focus on issues relating to the study design, conduct, reporting, and the results of the study

• applicability – the extent to which the evidence directly addresses a question

• consistency – the extent to which similar findings are reported using similar or different study designs and statistical approaches for a given question or outcome

Approaches to synthesis may vary according to the type of results being organised, described and explored. It is unlikely that meta-analysis will be performed in the context of an evidence summary.

Based on the synthesis, a judgement is made on whether criteria are:

• met – for example, in circumstances where there is enough evidence of sufficient quality to judge an outcome or effect which is unlikely to be changed by further research or systematic review

• not met – for example, in circumstances where there is not enough evidence to clearly judge an outcome or effect, or where there is sufficient evidence of poor performance

• uncertain – for example, in circumstances where the constraints of an evidence summary prevent a reliable answer to the question, for example when the need for a systematic review and meta-analysis is identified

4.3 Systematic reviews

Systematic reviews attempt to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a specific research question. Researchers conducting systematic reviews use explicit, systematic methods that are selected with a view aimed at minimising bias, to produce more reliable findings to inform decision making.

4.4 Cost effectiveness models

A cost effectiveness model is a mathematical framework to estimate the costs and health effects (that is the health outcomes, including benefits and harms) of a screening intervention compared with current practice, natural history of a disease, or another intervention, based on the best available evidence.

See UK NSC disease, clinical effectiveness and cost effectiveness modelling guidance.

4.5 Disease modelling exercises

A disease modelling exercise is a mathematical framework to estimate the health effects (or health outcomes, including benefits and harms) from a disease and interventions for the disease, based on the best available evidence. It does not compare with another screening programme or current practice.

See guidance on the use of modelling to support the work of the UK NSC.

4.6 Primary research

The National Institute for Health and Care Research (NIHR) defines primary research as experimental studies that generate new data.

The UK NSC research and methodology group (RMG) aims to:

• identify research requirements and prioritise research recommendations

• advise on mechanisms and methodologies to carry out and synthesise research on screening and on in-service evaluations

• establish close links with relevant stakeholders, for example funding bodies, researchers, and screening programme teams to ensure that the committee is up to date with screening research in the UK

4.7 In-service evaluations

In-service evaluations are used to test proposed new programmes or changes to existing ones. They involve the new or updated programme being implemented by NHS providers, during which data is collected to help answer specific questions on its operational impact and effectiveness. The evaluations are overseen by the Department of Health and Social Care (DHSC) screening team. They are designed with academic support to ensure the conduct of the study and the findings are sufficiently robust to support the UK NSC in making formal recommendations to ministers.

The results of in-service evaluations are used to support the UK NSC in making recommendations and to inform wider policy decisions.

If the UK NSC receives a topic proposal that has merit, then it requests an in-service evaluation if:

• the practical implementation of the proposal in routine NHS care would benefit from evaluation, and/or

• data from large scale programmes is needed

For example, an in-service evaluation is being undertaken on the use of self-sampling as a routine cervical screening delivery mechanism.

The UK NSC submits in-service evaluation requests to ministers for approval.

4.8 Stakeholder dialogues

A stakeholder dialogue is a process during which members of the public interact with scientists, stakeholders (for example research funders, businesses and patient representative groups) and policy makers to deliberate on issues relevant to future policy decisions.

For example, a public stakeholder dialogue considered the implications of whole genome sequencing (WGS) for newborn screening. That dialogue was commissioned by Genomics England and the UK NSC with support from UK Research and Innovation’s Sciencewise programme.

4.9 Evaluations of ethical issues

Decisions about any kind of NHS screening programme include an ethical element. Evaluations of ethical issues inform UK NSC recommendations in conjunction with evidence relating to other criteria, such as those addressing the reliability of the screening test, the effect of treatment and cost effectiveness.

See blog article describing work to embed ethics in the UK NSC’s processes and thinking.

5. Process

The UK NSC aims to ensure its evidence review process is proportionate and timely for all topics. The process provides reassurance to stakeholders that decisions are grounded in, and informed by, up to date evidence.

The following steps are also set out visually in the flowchart in section 3 above.

5.1 Identification

The UK NSC considers:

• topics on its regular list to review where there is an existing recommendation

• proposals for new topics (conditions or technologies) submitted via the annual call or other routes

• topics submitted via the annual call or other routes where new evidence is published which brings into question a current recommendation (an early update)

• proposals submitted via the annual call or other routes to modify, or make big changes to, a current screening programme (programme modification)

• topics for which NICE or SIGN suggest that an existing targeted screening guideline should be delivered through a nationally managed targeted screening programme

5.2 Filtration

Topics are checked to ensure they meet the fundamental criteria for consideration as a population or targeted screening programme.

Evidence maps (see definition in section 4 above) are used for the initial filtration of topics.

5.3 Prioritisation and assessment

The prioritisation process involves the selection of topics for further assessment, using more substantial evidence products.

The options for detailed assessment, illustrated in the flowchart, are:

• primary research

• systematic review

• modelling / cost effectiveness study

• evidence map

• evidence summary

• stakeholder dialogue

• in-service evaluation

• evaluation of ethical issues

Further assessment work is considered and conducted if the evidence suggests it is useful.

Once the detailed assessment has been completed it is shared with stakeholders through a public consultation process.

5.4 Consultation

The evidence review product(s) and associated documents for a topic are published on the UK NSC website and a 3-month public consultation exercise is conducted.

Registered stakeholders are contacted directly and invited to respond to consultations on all topics they are interested in. See UK NSC stakeholder engagement.

Any individual or organisation can respond to a consultation. The consultation web page includes guidance on how to submit responses.

5.5 Recommendation

The final evidence product(s) and consultation responses are presented to the UK NSC. The product(s) and responses then inform the committee’s decision on whether or not to recommend screening for the topic.

Evidence products can include research recommendations to address highlighted gaps in the evidence. Research recommendations are identified and prioritised in line with the terms of reference of the UK NSC research and methodology group.

6. Literature searches

A high-quality literature search is essential to reviewing the evidence on a condition against the criteria for a screening programme. This usually means searching a selection of appropriate bibliographic healthcare databases for published peer-reviewed research on the condition being reviewed.

The UK NSC literature search process follows a systematic approach in line with recognised academic standards.

Search strategies are designed by qualified information professionals, to appropriate standards and peer reviewed by colleagues (for example using PRESS guidelines). Searches focus on finding evidence to try to answer questions identified during the scoping process. These are framed around gaps identified from previous work (internal or external) on the topic and the UK NSC appraisal criteria for population, targeted or stratified screening. The number of questions varies and depends on whether a new topic is being assessed or if previous UK NSC work is being updated. For a new topic an overview of several criteria may need to be investigated. An update to a condition previously considered by the UK NSC may include fewer questions.

Sometimes the type of search strategy used may need to be adapted. Occasionally, highly structured searches of databases are not the best method and a more pragmatic or iterative approach might be taken. Examples of alternative approaches include hand searching reference lists of relevant articles or ‘citation pearl growing’, the process of using the characteristics of a relevant and authoritative article, called a pearl, to search for other relevant and authoritative materials, starting with significant publications. These methods should be agreed and justified at the protocol stage, be carried out systematically, and be described fully.

For the purposes of evidence maps and summaries, various methods can be used to limit the number of search results retrieved, for example the use of validated search filters to limit by study type. Any methods used to limit the number of search results should be noted as a limitation of the evidence product.

In the interests of transparency, a summary of the search strategy is an integral part of the main evidence document. This summary should include the databases searched, dates that searches were run, date limits of searches, number of results from each database, number of duplicate references removed, inclusion and exclusion criteria, who has carried out the sifting of results and any quality checks. A PRISMA-like diagram of inclusion and exclusion criteria should also be included in the search summary. Any limitations of the search should also be noted. Full details of the search terms used in each database should be included in an appendix.

1. Hines P, Hiu Yu L, Guy RH, et al. Scanning the horizon: a systematic literature review of methodologies. BMJ Open 2019;9:e026764 ↩