Effects of the Storage Solution Type and Prolonged Storage on the Immunoreactivity of Cells

In effusion cytology, immunocytochemistry is a useful staining approach to provide important information for diagnosis. Effusion cytology is performed not only for pleural effusions and ascites but also for peritoneal and needle washing from fine needle aspirations or instruments. Although various solutions are used for washing cytology, the effect of the solution type on immunocytochemical reactivity is not fully understood. In this study, we examined the immunocytochemical reactivity of cytological samples after storage in various solutions.

Cell block specimens were obtained from ascites of patients with peritoneal cancer and pleural effusions of patients with diffuse malignant mesothelioma. Various solutions, including physiological saline (PS), Ringer solution, a low-molecular-weight dextran L injection, Voluven 6% solution, Mixid L injection, RPMI-1640 medium, and horse serum were added to the sediment layers of aliquots. All samples were kept at 4°C, and aliquots were subsequently processed at specific time points (0, 1, 2, 4, 7, and 14 days). Formalin-fixed, paraffin-embedded, cell block samples were prepared for immunocytochemical staining. Immunocytochemical results were analyzed for differences in the percentages of positive cells, using the effusion sample stored for 1 h as standard (100%).

For all solutions other than PS, the median and central 50% of values were <100% (with respect to the effusion sample as a standard) after 1 h of storage. Immunoreactivity decreased for most solutions as time progressed.

Of note, immunocytochemistry results obtained using a washing solution are different from those using an effusion sample. For cytology, when a washing solution was used or when a sample was stored for a long time, the accuracy of the immunocytochemical results was low.