Diagnosis and Screening: Planning, operation and evaluation of screening programmes
Planning screening programmes
In the UK, the National Screening Committee (www.nsc.nhs.uk) advises the Government about the introduction and planning for new screening programmes. The NSC works closely with the Health Technology Assessment (HTA) Programme to review and commission research about screening effectiveness.
In addition to the effectiveness of the screening test, a number of other elements should be considered when planning a screening programme.
Screening programmes use one of two approaches:
- Opportunistic - screening is done as part of routine care when patients visit their doctors
- Proactive - the population targeted for screening are actively identified and invited to participate in the screening programme
Opportunities for effective early intervention created by screening programmes depend on the natural history of disease.
See earlier section about evaluating the performance of screening tests
The cost-effectiveness of a screening programme can be difficult to assess. There are a number of costs to consider.
- The cost of the test itself
- Costs of reading and interpreting the test
- Cost of diagnostic follow-up tests
- Cost of the programme management and data processing
- Cost of treating more cases that are identified due to the screening programme
- Cost of treating more advanced disease in the absence of a screening programme
- Opportunity costs for the health service and the individual
- Randomized controlled trials provide robust evidence for the effectiveness of a screening test, but the results may be difficult to reproduce in the real-world service setting.
- Variation in quality of service delivery may change the balance of harm and benefit of a screening programme.
- The final appraisal of whether or not to introduce a screening programme should ask whether a sufficient level of quality can be achieved at a reasonable cost, even if it does not reproduce the effectiveness achieved in a research setting.
- This balance between harm: benefit and quality of service delivery is summarized in the figure below.
Source: National Screening Committee (2000)
The role of the UK National Screening Committee
The National Screening Committee (www.nsc.nhs.uk) advises the Government about development and implementation of screening in the UK. Its role includes:
- Reviewing evidence about the effectiveness of screening
- Commissioning research on screening
- Advising on the introduction of new screening programmes
- Reviewing the continued delivery of screening programmes
- Assessing the quality of screening programme delivery
Principles of screening quality management
The Quality Management for Screening Project, published in 2000, lays out eight principles for screening quality management:
- A clear coherent framework of objective, standards, and guidance
- A culture of learning, not blame
- A partnership with staff and users
- Continuous Quality Improvement
- Clear management structures
- Performance should be measured effectively and efficiently
- Adequate systems and resources
- Bridging the expectation gap - informing the users, public, media, and staff about the benefits and limitations of screening
Operational steps to implementing screening programmes
In addition to playing a major role in the quality of screening programmes, the UKNSC is charged with ensuring effective implementation of screening programmes.
1. Invite target population
- Administer screening test
- Interpret result of the test
- Communicate results of the test
- Follow testing (as required)
- Treatment (as required)
- Data management systems
- Programme coordination, oversight, and quality assurance
- Ongoing monitoring and evaluation
Evaluating screening programmes
The National Screening Committee proposes 22 criteria (http://www.nsc.nhs.uk/pdfs/criteria.pdf) for appraising the viability, effectiveness and appropriateness of a screening programme. These draw on the Wilson and Jungner criteria and can be summarized as:
Is there good evidence (from systematic reviews or randomised controlled trials) that shows that early intervention in the disease improves outcomes?
- Is it safe?
- Will it work in our population and healthcare system?
- Is there an effective treatment that can be used following early identification of the disease?
- What are the benefits and harms of the screening programme?
- Is it cost effective?
Epidemiological artefact may increase the perceived benefits of the screening programme due to lead time and length time bias.
Lead Time Bias: When screening appears to increase survival time simply because the disease is detected earlier. Once this is taken into account, there may be little or no effectiveness of the screening test (i.e. improvement in survival time). For example, screening using prostate-specific antigen (PSA) test identifies prostate cancer in a patient at age 50 years but despite treatment he dies at 60 years. Without screening he might have been diagnosed at 57 years old and died at 60 years. Thus it falsely appears that survival is 7 years longer with screening, even though his survival is the same without screening.
Length Time Bias: An overestimation of survival because long-duration cases are more likely to be detected and treated than short-duration cases. For example, annual PSA screening is more likely to detect a slow-growing tumour of the prostate, which is also more likely to be detected while still at a treatable stage.
Screening programmes in development in the UK
In recognition that individuals may have more than one disease, and that some diseases may be interrelated, the National Screening Committee in the UK is developing five integrated population screening programmes. These are focused on different life-cycle stages:
- older persons
- Criteria for appraising the viability, effectiveness and appropriateness of a screening programme. (2003). London: National Screening Committee, UK
- Second Report of the UK National Screening Committee. (2000). London: National Screening Committee, UK
- Screening. (Accessed 4 June 2008) http://healthintelligence.bmj.com/hi/do/public-health/topics/content/screening/index.html
- Quality Management For Screening. Report to the National Screening Committee (2000) http://www.nsc.nhs.uk/pdfs/Quality-Management-for-Screening.pdf
© Dr Murad Ruf and Dr Oliver Morgan 2008