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11. Quality assurance, quality control and quality standards

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Quality assurance

The maintenance of a desired level of quality in a service [or product] especially by means of attention to every stage of the process of delivery or production



In order to maintain the desired level of quality in cervical cancer screening, the following systems are required:

Quality control: internal measures to ensure the accuracy of all stages of the process from date entry to the final report

Quality standards: measurements of laboratory practice that reflect good practice agreed at local, national and international level


Internal quality control systems (IQC) are applied by the laboratory on a daily basis such as in checks on data entry and technical procedures, and rapid review of primary screening.

External quality assurance systems (EQA) are applied by an outside regulatory body e.g. proficiency testing schemes, comparison of reporting rates and positive predictive values between laboratories, and accreditation.


Invasive cervical cancer audit

The final outcome of cervical cancer screening is the control of mortality and incidence of invasive cancer, but the numbers are low in local regions and screening centres so that monitoring cancer rates tends to be uninformative at that level.  However, much information can be gained from reviewing the full screening histories of women who develop invasive cancer, which identifies areas where screening procedures can be improved, and reasons why cancers are not always prevented by screening (Wiener et al. 2007).

Audit of invasive cancer is an integral part of the NHS Cervical Screening Programme (NHSCSP 2006a)


Reasons why invasive cancers may develop in screened populations (sometimes more than one reason in a single case)

  • Failure to screen the population at risk (system failures or non-compliance)
  • Screening carried out at irregular intervals, longer than recommended
  • Previous negative cytology (false negative or true negative)
  • Previous low-grade cytology not investigated (inappropriate recommendation, managed as recommended or non-compliance)
  • Referral recommended but cancer not prevented (system failures, lesion not found at colposcopy or non-compliance)
  • Treatment failures
  • Occult invasive cancers (usually IA or IB1) may be detected by cytological screening rather than prevented


Invasive cervical cancer audit

  • Identifies areas where screening procedures can be improved
  • Explains reasons why cancers are not always prevented by screening