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.
Skin Scraping. This technique is used to rub cells off the surface of the skin. It can be used, for example, on a patch of flaky skin, a bald spot, or an ulcerated bump. With 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 the top layers of skin cells. 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 any discomfort.
Impression Smears. When there is a draining wound or an oozing sore, 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 crusting or build-up of surface debris, impression smears are often made twice – before, and after, gently cleaning the area to remove the crust and debris. Impression smears, like skin scrapings, are good for detecting the presence of inflammation, infectious organisms, and abnormal tissue cells.
Swabs. A swab (usually cotton-tipped) is used to collect discharge from moist surfaces like the mouth, eye, ear, nostril, prepuce, and vagina. The swab is wiped firmly across the affected area and then rolled against a glass slide so the cells adhere to the slide. The resulting smear often reveals inflammatory cells, infectious organisms, and small numbers of tissue cells from the surface that can be examined for signs of abnormality.
Flushes. This specialized technique is used to collect cells from surfaces within the body, such as the nasal cavity, trachea (windpipe), lungs, or prostate gland. The pet is usually placed under sedation or anesthesia, and a thin, flexible, and 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 a small number 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?
The examination of surface cells is often helpful, and in some circumstances can provide a definitive diagnosis. However, in many cases, the surface cells do not tell the whole story, and additional samples must be collected from the tissues 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 "Fine Needle Aspiration (FNA)" for further information.