Technical external quality assessment for SurePath stained liquid-based cytology gynaecological cervical samples...

The Technical External Quality Assessment Scheme (TEQA) introduced in Wales is based on NHSCSP publication No 19 [External Quality Assessment Scheme for the Evaluation of Papanicolaou Staining in Cervical Cytology] which sets out the policies and standard operating procedures for the TEQA of Papanicolaou staining of gynaecological cervical samples. As part of a development plan for the TEQA scheme in Wales, the use of a control sample was introduced to the assessment process - a common control sample can provide a consistent assessment parameter independent of the recommended slide selection process [External Quality Assessment Scheme for the Evaluation of Papanicolaou Staining in Cervical Cytology, NHSCSP Publication No 19, February 2004] enabling direct comparison of staining standards for laboratories within the region; this counters selection variation bias, establishing a process that may be more representative of routine staining results.

A cervical sample was selected in line with the criteria described in publication 19 [External Quality Assessment Scheme for the Evaluation of Papanicolaou Staining in Cervical Cytology, NHSCSP Publication No 19, February 2004]. Thirteen slides were prepared by the scheme facilitator from this anonymized sample. These control slides were subsequently 'fixed' but not stained, then distributed to the laboratories participating in the TEQA scheme. The slides were stained using their standard regime, then returned to the facilitator for assessment. The slides showed consistent staining with no significant inter-laboratory variation, however, the eosinophilic stained components exhibited an artificial colouration, which slightly altered the expected stained appearance; this was thought to be due to 'cross-reactivity' of the spray fixative with the preserving agent. To address this artefact, a further development of control procedures was devised utilizing a pooled control sample procedure. Residual material from a number of similar samples was pooled and distributed in aliquots to participant laboratories for standard processing and staining; the completed slides were returned to the scheme facilitator for assessment.

The pooled sample slides were assessed at the next scheduled quarterly TEQA assessment. The overall scoring for these samples produced an acceptable level of Papanicolaou staining for 12 of the laboratories - only one laboratory produced a marginal score. The artefactual presentation of eosinophilia was not seen.

This method of producing control material establishes consistency in the TEQA comparative assessment process, counters selection bias and reduces the time demands associated with slide selection. It may also prove useful in identifying technical problems within laboratories during sample preparation prior to or during staining, including equipment or process faults. This technique is now well established locally as an enhancement of the current TEQA scheme for the assessment of slide staining. We feel that this enhancement could be incorporated as a new initiative in the current National TEQA scheme as a complement to the established selection process.