Impression smear and swab cytology in cats and dogs
An impression smear, swab or tape test collects cells from the surface of the skin, an ear, a wound or a moist membrane and looks at them under the microscope. It is quick and gentle and often answers whether there is inflammation, bacteria or yeasts — but it shows only the surface, so it is a clue for the vet rather than a diagnosis.
What it shows
For an impression smear or swab the vet collects cells from a surface, stains them on a glass slide and examines them, often in the clinic. Ways of collecting differ by site:
- Impression smear — a clean slide is pressed onto a draining wound or oozing sore and lifted off, several times. If there is a crust, impressions may be made before and after cleaning.
- Swab — a cotton-tipped swab collects discharge from moist surfaces such as the ear, eye, nose or mouth and is rolled onto a slide. Ear samples are taken before the ear is cleaned.
- Tape preparation — clear acetate tape is pressed to the skin, which suits dry areas and skin folds.
- Scraping with a slide edge — for flaky or crusted skin and claw folds. In itchy animals, material from under the nail beds may also be smeared.
Higher than reference — what it may be a sign of
- Bacteria — round bacteria (cocci) are usually staphylococci or streptococci; rod-shaped bacteria may be Pseudomonas, E. coli and others. Bacteria inside neutrophils show that they are causing infection, not just sitting on the surface.
- Yeasts — Malassezia look like small peanuts or snowmen. A few are normal in the ears of healthy dogs and cats; in ear inflammation they often multiply.
- Neutrophils — not normal in the ear canal; many neutrophils with engulfed bacteria confirm an infection.
- Eosinophils — may point to parasites, fungi or food allergy.
- Acantholytic cells — rounded “fried egg” skin cells that have come apart from each other; mainly linked with immune-mediated skin disease such as pemphigus, but severe bacterial infection and ringworm can also produce them.
- Abnormal cells — for example large atypical lymphocytes, consistent with skin lymphoma, or mast cells from an ulcerated mast cell tumour.
- Ear mites — eggs, larvae and adults are looked for in ear material mixed with mineral oil, at low magnification.
Each finding is an observation for the vet, not a diagnosis.
Lower than reference
A report with few cells or “no organisms seen” is not a guarantee that all is well. A surface sample shows only the top layer and may miss what lies deeper. Mites are seen in a smear only when there are many of them. When the surface sample does not explain the problem, the next step may be a fine-needle aspirate from deeper tissue or a biopsy for histology.
Look at together with
- Skin scrapings and other tests for ectoparasites — scrapings are used mainly to look for mites, cytology for bacteria and yeasts.
- Bacterial culture and susceptibility — when rods are seen, when infection keeps coming back, or when the vet needs to know which antibiotics work in the lab.
- Ringworm (dermatophyte) testing — fungal spores can be seen on cytology, but ringworm is confirmed by other tests.
- Repeat cytology — with ear infections the vet may repeat the smear every one to two weeks until it shows no more infection.
Units and conversion
There are no units: the result is a description of what the cytologist or the vet saw. The report names the cells and organisms found and estimates their amount in words; the format differs between clinics and laboratories. In the app the result is kept as text, the way it is written on the form.
Reference range
The reference range is on your lab’s form — or rather, there is no number to compare with. Healthy skin and ears may show surface skin cells and small numbers of bacteria and yeasts; what matters is the pattern: many organisms, organisms inside neutrophils, neutrophils in the ear, or cells that do not belong there. Routine quick stains do not tell Gram-positive from Gram-negative bacteria, and melanin granules can be mistaken for bacteria.
Cats and dogs
Eosinophils are common in skin cytology of cats, so their presence is read differently from dogs. In a cat with dark, “coffee-ground” ear discharge, ear mites (Otodectes cynotis) are strongly suspected and are looked for in the ear material. Low numbers of Malassezia can be found in healthy cat ears.
In atopic dogs eosinophils are rarely found on skin cytology. Small numbers of cocci and Malassezia are normal in the dog’s ear canal; in ear infections the rods seen are usually Pseudomonas aeruginosa, E. coli, Proteus mirabilis or Corynebacterium, and ulceration with slimy green discharge and only rods strongly suggests Pseudomonas.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- VCA Animal Hospitals — Cytology: collecting cells from surfaces
- VCA Animal Hospitals — Cytology: general
- Merck Veterinary Manual — Diagnosis of skin diseases in small animals
- Merck Veterinary Manual — Otitis externa in animals
- Merck Veterinary Manual — Cytology (diagnostic procedures for the private practice laboratory)
- eClinPath (Cornell University) — Cytology: sample collection
- Today’s Veterinary Practice — Dermatology diagnostics: cutaneous cytology (C. Reeder, 2017)
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.