What is cytology?

Cytology is the microscopic examination of cells that have been collected from the body. By examining the appearance of these cells, including their number, size, shape, color, internal characteristics, and how they fit together with their neighbors, it is often possible to make a diagnosis of a specific disease process.

How are cells collected from body surfaces?

There are different methods for collecting cells from body surfaces, and each is used in slightly different circumstances:

a)  scrapings

b)  impression smears

c)  swabs

d)  flushing or lavaging

a)  Skin Scraping: dragging cells off

This technique is used to pull cells away from the surface of the skin, for example, when there is a patch of flaky skin, a bald spot, or an ulcerated skin bump. In this technique, a sterile scalpel blade is held at right angles to the skin and firmly dragged across the skin surface several times, scraping away a few of the top layers of skin. The material that accumulates on the scalpel blade is spread thinly on a glass slide. The slide is then stained with special dyes and examined under the microscope. This technique is good for detecting the presence of skin parasites, bacteria, yeasts, fungi, inflammatory cells, or abnormal skin cells. The skin may bleed a little after being scraped, but the wound is minor, no more than a scratch, and usually does not cause the pet any discomfort.

b)  Impression Smears: lifting cells off

When there is a draining wound or an oozing sore on the skin, impression smears are used to collect the surface material so that it can be examined more closely. Impression smears are made by pressing a clean glass slide firmly against the affected area and then lifting it away. This action is repeated several times, and each time a small amount of material adheres to the slide. If there is a lot of crusting or build-up of surface debris, impression smears are often made twice - first before cleaning the site, and then after the surface crust has been gently wiped away with sterile gauze. Impression smears, like skin scrapings, are good for detecting the presence of inflammation, infectious organisms, and abnormal tissue cells.

c)  Swabs: wiping cells off

A swab (usually cotton-tipped) is used to collect discharge, and to harvest cells from moist surfaces like the mouth, eye, nostril, and vagina. The swab is wiped firmly across the affected area, and is then rolled against a glass slide so that the cells adhere to the slide. The resulting smear usually reveals inflammatory cells, infectious organisms, and small numbers of tissue cells from the surface that can be examined for signs of abnormality.

d)  Flush (Lavage): washing cells off

This specialized technique is used to collect cells from surfaces within the body, such as the nasal cavity, trachea (windpipe), lung. The pet is usually placed under sedation or anesthesia, and a thin, flexible, sterile catheter is passed into the area being investigated. A small amount of sterile fluid is flushed forcefully into the area and then promptly suctioned or aspirated back out. The recovered fluid contains small numbers of cells that can be examined. A flush or lavage is often helpful to identify inflammation, infection, and cancer.

Are cytology samples collected from surfaces always diagnostic?

Examination of surface cells is often helpful, and in some circumstances can provide a complete diagnosis. However, in many cases, surface cells do not tell the whole story, and additional samples must be collected from tissue below the surface. This usually requires a technique called fine needle aspiration or fine needle biopsy, which involves the use of a fine gauge needle attached to a syringe to aspirate or remove cells from below the surface (see handout "Cytology - Fine Needle Aspiration").