• Overview
• Definition
• Health consequences
• Costs
• Contributors

Overview

Screening has the potential to save lives and improve quality of life through early diagnosis of serious conditions such as breast cancer and cervical cancer. Screening of newborns can detect genetic or congenital conditions, thus minimising the irreversible damage that can affect a small number of babies. Very occasionally, screening may provide information to make informed choices in cases where the condition is not treatable, for example, genetic screening may inform reproductive decisions in the case of Down’s syndrome.

Screening is targeted at apparently healthy people who are given the opportunity to make informed choices about improving their health. Most people who are screened believe that prevention is better than cure and expect to be given a clean bill of health. Individuals who have disease detected as a result of screening usually believe that they have been saved from a more serious condition by the early intervention. ^{1 2}

Screening reduces the risk of developing a condition or its complications, but it cannot offer a guarantee of protection. ³ It is rarely possible to guarantee that an individual will benefit personally from taking part, and screening can lead to a level of anxiety. ‘Some screening programmes can help, all screening programmes can harm’ ⁴ and some unnecessary screening, such as whole body CT, can lead to more serious consequences. ⁵

Understanding the criteria and components of a screening programme is therefore a key part of public health to ensure that the benefits of screening outweigh harms at a population level.

Criteria for screening programmes

Overview of criteria

The UK National Screening Committee (UKNSC) established 22 criteria for ‘appraising the viability, effectiveness and appropriateness of a screening programme’. ⁶ A summary of these criteria for screening programmes are given in Box 1. These criteria are used to advise Ministers on implementing new population screening programmes and screening technologies, and modifying or withdrawing existing population screening programmes of doubtful effectiveness, quality or value.

The criteria for screening given in Box 1 are based on Wilson and Junger’s report for the World Health Organisation on screening. ⁸ This report was the first to recognise that screening only appears simple and that there is much scope for harm. Wilson and Junger produced ten ‘guides for planning case-finding’ by which a potential screening programme may be assessed. ⁸

Natural history of disease

Screening aims to detect and intervene at an early stage in the disease pathway in order to reduce ill health. Screening can take place at various stages; however, effective early intervention requires an understanding of the natural history of the disease. Table 1 gives examples of interventions at different stages in a disease pathway, and which could be considered to be screening.

Uncertainties

It is important to bear in mind that screening is a complex process and there are uncertainties at various stages of the pathway. For example, who should be screened, how to define the target population (see Key components section) and how long is the recall interval. For instance there is good evidence that breast screening for women aged 50-70 saves lives and is cost effective ⁹ , but screening women aged 40-49 is likely to do more harm than good.(See External Link ) ¹⁰

Key components

The key components of a systematic screening programme are listed as follows.

Identify and systematically invite the target (apparently healthy) population

The age range and gender of the target population is defined for practical reasons of capacity and cost-effectiveness, or because the test results may be harder to interpret in a wider population. This does not, however, imply that the disease or risk does not occur outside that defined target population (see example in Box 1). Invitations for screening may be generated from primary care records or voting lists for adults, women booking for obstetrics for antenatal and newborn screening, or even from disease registers, for example, for diabetic retinopathy.

Screening test

A simple test is required to identify those who may have the disease or defect from those who probably do not.

Administration of screening test

This involves taking a tissue sample, such as blood from a pregnant woman or a newborn baby, or an image, such as retinal photography or mammography.

Reading and communicating result

Images would have to be examined or the sample analysed by a qualified health professional, such as radiologists, using appropriate equipment. A process for communicating the results back to each person screened, preferably in writing, is also needed. It is not acceptable to expect people to assume that ‘no news is good news’.

Follow-up procedure

Ongoing assessment and diagnosis of those who screen positive (i.e. those who probably have the disease) is required. Interventions to treat the condition may be more effective at this stage than if diagnosed once symptoms have developed.

Referral for prompt treatment

It is unethical not to treat screen-detected disease promptly and the benefit of early detection may be lost by delay. Newborn babies with congenital hypothyroidism need to commence treatment within a few weeks of birth if irrevocable harm is to be prevented.

IT system

Population screening programmes involve maintaining accurate and secure records of many thousands of individuals who need to be tracked through all the stages of the screening process and reinvited appropriately. A small proportion of lost records could result in considerable harm. For instance, 1.5 million people with diabetes are offered retinal screening annually and those newly diagnosed added promptly.

Management of the screening programme

The whole screening process is complex and involves a multidisciplinary team, working with large numbers of people being screened. Effective management should ensure systems are in place to ensure that no one is missed out or left without completion of the whole episode, e.g. all those who screen positive have timely appointments for further investigations.

Integral quality assurance (QA)

It is important to ensure that all the above features are working to high standards. In addition,

standards must be set and achievements monitored against them regularly. A system must be in place to ensure reliable results by checking, especially where tests involve visual perception.