Rehydration before wet fixation in conventional body fluid cytology - An 18-year experience

Purpose: In conventional cytology, preparation of a specimen by wet fixation for Papanicolaou stain is potentially subject to dry effect or cell loss which may make cytologic interpretation difficult or even impossible. We have been routinely making an additional smear for rehydration with normal saline (rehydration method) before wet fixation to overcome the above shortcomings.

Methods: We reviewed malignant pleural effusion and ascites 15 cases each in our cytology laboratory over the past 1 year. Four slides of each specimen were made. Two were air-dried for Liu's stain (a Romanowsky stain) and the other two were wet-fixed for Papanicolaou stain. The air-dried smears were also served as retained cellularity control. One of the two wet-fixed smears was processed as a control of preservation of nuclear detail whereas the other one stayed air-dried for 10 minutes and then covered with normal saline (rehydration method) for 80 seconds before wet fixation.

Results: There was minor cell loss (P = .032). The cells appeared larger with good preservation of nuclear detail (P < .0001 by two-sided Wilcoxon rank sum test) but no red blood cells retained on the slide after rehydration.

Conclusion: The rehydration method can effectively minimise cell loss, enlarge and preserve the cytological features of malignant cells with haemolysis. This method is simple, practical and good for cytological screening for tumour cells and interpretation especially in a bloody smear. We recommend that the rehydration method be part of traditional cytopreparatory work of wet fixation for Papanicolaou stain in conventional body fluid cytology.