External quality control for immunocytochemistry on cytology samples: a review of UK NEQAS ICC (cytology module) results

External quality control for immunocytochemistry on cytology samples: a review of UK NEQAS ICC (cytology module) results Objective: To date, external quality control for immunocytochemistry on cytology samples is provided only by the United Kingdom national external quality assessment service for immunocytochemistry and in situ hybridisation (UK NEQAS ICC & ISH). For the purpose of this study a retrospective analysis of a comprehensive collection of quality-related data regarding immunocytochemistry on cytology samples collected through this service was analysed. Methods: The quality of immunocytochemical reactions, using on-line collected data, was analysed for the last 23 UK NEQAS ICC cytology module external quality assessments carried out on cytology samples completed in the period from 2004 to 2010. Results: Our study showed that the majority of participants in the cytology module (66%) sent formalin-fixed paraffin-embedded (FFPE) tissue sections for assessment as in-house control slides and only 34% sent cytology slides of various types. The highest UK NEQAS ICC score for the quality of immunocytochemical staining among in-house control slides was achieved on cell block sections, followed by cytospins, FFPE tissue sections, liquid-based cytology slides and smears. With regard to fixation, acetone-fixed slides achieved significantly lower scores than other reported fixatives. The strength of agreement in perception of immunocytochemical staining quality was good between in-house assessors (Kappa = 0.64) but only fair between in-house and UK NEQAS ICC assessors (Kappa = 0.22). Conclusions: Good quality of immunocytochemical staining can be achieved on cytology slides prepared and fixed in different ways as well as on cell blocks. Unified criteria for high-quality immunocytochemical staining and proper internal and external quality assurance could facilitate further improvement and standardization of immunocytochemistry on cytology samples.