Canine Vaginal Cytology
Canine Vaginal Cytology

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  • Moisten a cotton swab with 1 to 2 drops sterile saline. Open the vulvar lips, pull the vulva doraslly, insert the swab dorsally and posterior, then up and over the pelvic brim and into anterior vagina. If you do not pass the swab far enough, you will get vestibular cells and result in false cornification. If you pass the swab too ventral, you may enter the bladder and get a falsely non-cornified smear.
  • Roll the swab firmly onto a slide.
  • Stain the slide using DifQuik stain, 10 dips in A, 15 dips in B, and 20 dips in C. You may also use new methylene blue stain.
  • Read the slide under low power first to establish the trend of cellularity and cell types. Move to a higher power to establish the cell types. View several fields to get an overall visual idea of the percentage of cornified cells.


Click on the movie icon, then right click on the movie or "Open It" and "OK" to see
a Vaginal Cytology Exam performed
Vaginal Cytology Cell Types
  • Parabasal cells have a large stippled nucleus and a rounded cytoplasm The nucleus is large compared to the cytoplasm.
  • Intermediate cells have a have a stippled nucleus and more cytoplasm than parabasal cells. The cytoplasm may even become angular.


Superficial cells have a pyknotic nucleus and angular cytoplasm.  There is no stipling in the nucleus.

Anuclear cells have no visible nucleus and angular cytoplasm.

Remember 'PISA'

Click picture above to enlarge the cells.

Changes during the estrous cycle
  • When no estrogen is present (anestrus and diestrus, the vaginal wall is very thin and is comprised of noncornified cells. In anestrus there will be very few cells and what you see will be debris and non-cornified cells.
  • When estrogen rises during proestrus, the vaginal epithelium becomes hyperplastic and more cornified. During proestrus the percent of cornified cells increases by about 10%/day until you see  about 100% cornification during estrus. You may also see RBCs during proestrus.
Thin vaginal epithelium during anestrus.
  • During estrus the vaginal epithelium is very thick. You will see almost 100% cornification. The smear will look the same from the first day of estrus of the last day of estrus, You cannot tell which day of estrus the bitch is in based on vaginal cytology. There may however, be some sheeting of cells during the last 1-2 days of estrus. The vaginal wall is so thick during estrus that PMNs do not cross the epithelium. This makes the background look very 'clean'.

Estrus smear with 100% cornification and a clear background.

Sheets of cells during the end of estrus.

  • On the first day of diestrus the cells in the swab abruptly change to around 50% non-cornified. This day that the smear changes from 100% cornified cells to 50% non-cornified cells is denoted as the first day of cytologic diestrus. You may see an influx of PMNs at this time to help clean up all the cellular debris.

Abrupt change to non-cornified cells on the first day of diestrus.


Link to CSU practice set of vaginal cytology cases by clicking here.

Click here to see a PowerPoint Auto tutorial on Canine Vaginal Cytology

contributed by Bruce E Eilts and modified on 29 August 2006
modified by
Eric Huey and Emma Jones


contributed by Bruce E Eilts on 25 September 2012


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