Vaginal cytology is a microscopic examination of cells from the vaginal epithelium. In veterinary medicine, it helps differentiate the stages of the mammalian estrous cycle because the vaginal epithelium changes in response to sex hormone levels; practically, it is used to distinguish when a female canine is at a particular point in the estrous cycle.[1] In a normal vaginal smear, lactational cells, navicular cells, endocervical cells, endometrial cells, trophoblastic cells, and leucocytes may be present.
The equipment needed for vaginal cytology includes a vaginal speculum, cotton-tipped applicators, frosted microscope slides, commercial Romanowsky stain, and light microscope.[2]
Estrus is characterized by the presence of all superficial cells, many of which are anuclear (without a nucleus) or have small, pyknotic nuclei, and red blood cells may be present, along with bacteria. No neutrophils are seen unless there is inflammation. There is usually no mucous in the background.[3]
Indiestrus, superficial cells are replaced by parabasal and intermediate cells within one to two days of onset.[2] Neutrophils are increased. Red blood cells may be absent or present. Bacteria is commonly observed. A smear made during late estrus to early diestrus may appear similar to one made in early- or mid-proestrus.[2][3]
The final stage of estrous is anestrus, which is characterized by predominantly non-cornified squamous epithelial cells, such as intermediate or parabasal cells. The cells are smaller, have basophilic cytoplasm, and large round nuclei. There may be some neutrophils, but no red blood cells. The overall cellularity is low.[2][3]
