CHAPTER 22 Cervical screening programmes
Chapter contents
Introduction
In the middle of the twentieth century, screening for cervical cancer was heralded as the solution to a type of cancer that had hitherto been almost invariably fatal. Yet it has taken the best part of the latter half of that century to see falls in incidence and mortality in those countries that have well organised screening programmes. This chapter will address the problems and some of the solutions to running a cervical screening programme and will explore some of the recent developments that could be used to enhance the screening procedure.
Principles of screening
Screening can be defined as the testing of people who do not have any recognisable signs of the condition in question, with the purpose of reducing risk for that individual of future ill health due to disease. Screening encompasses the whole system and is a programme not a test.1
Screening for disease in a population might seem to offer obvious benefits, but as Raffle and Gray have stated, ‘All screening programmes do harm. Some do good as well and, of these, some do more good than harm at a reasonable cost’.1 The aim of any screening programme is to detect disease at an earlier stage than it could have been detected by symptomatic presentation, but clearly the disease is only suitable for screening if the benefits outweigh the harms in this equation.
History of cervical screening in the UK
George Papanicolaou had described cytological changes in cervical smears in 19282 but his technique was not widely implemented for many years. It was not until the 1950s that cervical smears were first taken in the UK, but there was no properly organised programme. Screening tended to concentrate on young women attending for contraceptive and antenatal care, predominantly from higher socioeconomic groups. These women were at low risk of cervical carcinoma and women continued to die of the disease in undiminished numbers. It became apparent, however, that in areas where a well-organised programme was in place, for example Scotland,3 mortality began to fall.
However, although the programme was much improved it became apparent that there were still a number of problems. A series of errors were highlighted in very critical reports, culminating in the investigation into screening services at Kent and Canterbury which was published in 1997.4 This defined the need for robust quality assurance (QA), which is one of the main features of the programme today.
There is now abundant evidence that the UK cervical screening programmes have greatly reduced the incidence of cervical cancer5–7 and this reduction appears to be continuing, although the rate of improvement may be decreasing. There is also evidence that without screening, the incidence of cervical cancer would be increasing dramatically, so that it is now calculated that 75% of cases are prevented, saving thousands of lives per year in England and Wales (Figs 22.1, 22.2).5
The UK cervical screening programmes
Delivery at a local level involves many individuals and organisations whose roles are described in Box 22.1.
Box 22.1 Roles of organisations in the English cervical screening programme
Primary care trust (PCT) • Responsibility for governance of sample takers, some as direct employees, others through normal governance routes for general practitioners | Cytology laboratory |
Colposcopy • Investigation and treatment of women with abnormal cervical samples according to national quality standards | Histology laboratory |
Sample takers |
Quality assurance and governance
The responsibility for commissioning cervical screening lies with the local Primary Care Trust (PCT), and the overseeing and performance management of this role rests with the Strategic Health Authority (SHA) for that Region. Responsibility for performance of parts of the service delivered within hospitals rests with the NHS Trust concerned, ultimately with its Chief Executive. All professionals working within the programme have a responsibility to ensure they have been adequately trained and are conversant with the programme.
Large scale ‘look back’ exercises when mistakes emerge are very damaging to morale within the service and to uptake of screening by women, for whom there is often considerable distress. The greatest success of the QA process is that since this was fully established in 1996/1967, these enquiries have largely been avoided. Key outcome measures reviewed by the QA process are summarised in Table 22.1.
Table 22.1 Outcome measures in cervical screening quality assurance
Outcome measure | Description | Acceptable value |
---|---|---|
Coverage | Eligible population having an adequate sample in the last 5 years | 80% |
Laboratory sensitivity | Abnormal samples recognised as such (detected by rapid re/preview) | 90% all grade; 95% high-grade dyskaryosis |
Positive predictive value (PPV) | Proportion of women with cytology result of moderate dyskaryosis or worse who have CIN 2 or worse on histology | 10th–90th centiles of all laboratories; 70.7–88.9% (2007–2008)6 |
Detection rates for abnormalities | Proportion of samples taken in a primary care setting reported as abnormal by each laboratory | 10th–90th centiles of all laboratories; Low grade 3.6–7.4%; High grade 0.7–1.4%8 |
In conclusion, the NHSCSP is a process which is specified in detail9 and fully quality assured. It is a national, lifelong process for women, interlinking all disciplines with fail-safe processes at every stage where intervention is required.
Comparison with other national cervical screening programmes
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