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The use of control samples in the PAPANICOLAOU technical external quality assessment scheme

Abstract

Technical external quality assessment (TEQA) in Wales is based on NHSCSP publication 19, which sets out policy and procedures for the scheme. The purpose of EQA is to sustain and improve the quality of patient care by promoting a high standard of performance. Following the introduction of liquid base cytology (LBC) technical limitations, particularly in assessing counterstaining, have been noted. LBC provides the means to address these limitations ‐ As part of a development plan for TEQA in Wales, a control sample procedure was introduced to the scheme. A pooled control sample was composed, containing residual material from six ‘matched’ negative samples, re‐suspended in collection fluid. Aliquots of this sample were distributed for processing and staining, to the 13 laboratories registered with the scheme. The slides produced were assessed at a scheduled TEQA assessment in accordance with the standard criteria. Initial overall scoring for these control samples produced acceptable levels of staining for 12 of the laboratories ‐ one laboratory produced a marginal score. Repeat distributions have shown maintained or improved results. This method provides a prospective quality assessment tool, which counters the emphasis on slide selection and eliminates potential selection bias, whilst introducing consistency and improving comparability across participant laboratories. The method may also prove helpful in identifying technical inconsistencies such as equipment or handling errors that may occur during sample processing prior to or during staining. The control process, which is now used routinely in the Welsh TEQA scheme; is considered complimentary to, and not a replacement for, the selection process established in NHSCSP #19. However, we feel that this development could be considered as a new initiative in the National TEQA scheme. The control process is applicable to all LBC systems in current use.