Cytology screening

Cytology screening with the familiar Pap smear has been the mainstay of cervical cancer screening for many years. The Pap test is the only test known to reduce cervical cancer incidence and mortality in programmes, particularly organized population screening programmes. Data from the Nordic countries have shown that well-organized cytology screening programmes have reduced mortality from cervical cancer by approximately 60%. However, such reductions are seen with organized population-based screening, and not with opportunistic unorganized screening.

Strengths of cytology screening include the decades of experience in its use, a high specificity, its adaptability to computer-assisted reading, the lesions identified are easy to treat and its relatively low cost.

Limitations of cytology screening are that the test is difficult to comprehend in many cultures, the test is invasive and potentially embarrassing, trained personnel are required, smear adequacy is not intrinsically obvious, it is necessary to recall women for further tests if the results are not clearly negative, the test has only moderate sensitivity, cytology is unable to distinguish progressive disease from that destined to regress, and it is impossible by screening to eliminate all cervical cancer mortality.

Organizational aspects are paramount in the conduct of an effective population screening programs. The fundamental organizational components are:

• Effective leadership and centralization of decision making;
• Management and oversight of all phases of the programme;
• Attention to and linkages between all levels of the programme; and
• Realistic budgeting for each component of the programme.

Essential elements for a successful cytology screening programme include:

• Training of the relevant health care professionals, including smear takers, smear readers (cytotechnologists), cytopathologists, colposcopists and programme managers;
• An agreed decision on the priority age group to be screened (initially 35-54);
• Adequately taken and fixed smears;
• Efficient and high quality laboratory services, that should preferably be centralised, quality control of cytology reading;
• A means to rapidly transport smears to the laboratory;
• A mechanism to inform the women screened of the results of the test in an understandable form;
• A mechanism to ensure that women with an abnormal test result attend for management and treatment;
• An accepted definition of an abnormality to be treated,  i.e. high grade lesions;
• A mechanism to follow up treated women;
• A decision on the frequency of subsequent screens;
• A mechanism to invite women with negative smears for subsequent smears.

Elements that interfere with the development of successful cervical screening programmes are:

• Over-reliance on maternal and child health services for screening, especially for defining the target group;
• Opportunistic (spontaneous) screening, often focusing on frequent screening of low risk women;
• Low compliance with screening of the target group (evaluation by counting smears, rather than counting women screened); and
• Setting too low a threshold for referral for colposcopy (over-treating non-progressive disease).