Validation of on-slide immunocytochemistry controls prepared from long-term preserved prefixed cell suspensions

On-slide controls are essential for quality assurance in immunocytochemistry, yet their use in non-cell block cytology preparations remains a significant challenge. This study presents and evaluates a novel method for preparing on-slide controls from long-term prefixed cell suspensions, applicable to all types of cytology preparations.

A methodology for preparing on-slide controls is described in detail and comprehensively validated via three key evaluations: assessing antigen and cellular morphology stability in 17 suspensions over 29 months; conducting a retrospective review of immunocytochemistry records (2019-2024) to determine feasibility; and performing a tracer study to evaluate cell carryover risk.

In the stability assessment, all 20 evaluated antigens and cellular morphologies remained well preserved in the stored control samples, with only transient partial loss of antigenicity observed on three of 149 slides. The method was successfully and reliably applied in 1904 immunocytochemistry tests (n = 48 primary antibodies), with a failure rate of 0.3% (95% CI, 0.1%-0.7%). The dedicated tracer study confirmed the complete absence of cell carryover or cross-contamination.

The described method offers a robust, practical, and adaptable solution for preparing on-slide controls applicable to all cytology preparations, including previously stained and mounted slides. Implementing this approach strengthens quality control for non-cell block cytology slides, enhances diagnostic reliability, and brings cytology practice closer to the quality standards established in immunohistochemistry.