EXPRESS: Vaginal Cytology in the Queen: Clinical and Cytological Correlations

Objectives: Vaginal cytology has a broadly recognized value for estrous cycle staging due to the responsiveness of the vaginal epithelium to estrogens causing changes in the cellular pattern. Unlike the bitch, vaginal cytology is not routinely used in queens. The aim of this study was to characterize vaginal cytological patterns and standardize its interpretation in female cats. Methods: Thirty-nine vaginal smears were collected from 33 intact queens using a simple and quick procedure with little if any physical restraint, analyzed for cellularity, clearing, epithelial cell types, and the presence of red blood cells or neutrophils. Queens were classified in different estrous phases based on reproductive history and serum progesterone levels. Results: The 39 vaginal smears were classified as proestrus (N=1), estrus (N=9), interestrus (N=10), diestrus (N=9) and anestrus (N=9). One vaginal smear was not allocated to any cycle phase because the queen was diagnosed with pyometra. Cellularity was poor in 21/39 smears from which 8 were from queens in estrus. Cytological estrus was characterized by ≥ 90% keratinized epithelial cells, unlike previously reported, and presence of clearing in scarce to modestly cellular smear. Conclusion and relevance: Progesterone concentration is needed to differentiate interestrus from diestrus due to the mixed cell population on vaginal cytology. Keratinized vaginal cells are consistently found in anestrus smears of queens and should not lead clinicians to assume the queen is cycling. Neutrophils can be present in the different estrous cycles in cats without being associated with clinical signs of disease, unlike red blood cells. These findings demonstrate that vaginal cytology can be a useful tool in feline practice for managing reproductive presenting complaints.