6 ways to collect cells for cytology

Cytology is an essential tool available to all of us in veterinary practice. There are numerous ways in which to collect your sample, and in this article we look at the 6 most effective techniques.

Posted: 07 March 2018

6 ways to collect cells for cytology


1. Fine needle aspirates (FNA) - collecting the perfect sample

This is the most frequently used sampling technique and is the ideal way to collect a representation of cells from local masses and internal organs due to it being noninvasive. In order to collect the best sample, you need a good technique.

Below is our simple guide to the perfect FNA;

  • Advance the needle – carefully insert the needle into the mass and apply gentle negative pressure using the syringe. Whilst holding the negative pressure, redirect the needle several times in order to obtain a representative sample. Don’t over aspirate in an attempt to fill the hub of the needle. In most instances when performing a FNA the sample rarely fill more than the bore of the needle. Often nothing is visible in the needle hub and syringe.
  • Release the pressure – it’s most important to release the pressure on the syringe plunger before removing the needle from the mass to avoid over aspirating and sucking the cellular sample into the syringe itself.
  • Expel the sample - after withdrawal, the needle can be removed. Fill the syringe with air and then reattach the needle. Push on the plunger and expel the contents of the needle onto several slides.
  • Prepare the slides - samples are prepared by laying a clean slide on top of the sample and drawing the two slides apart. The aim is to smear the cells thinly and in a smooth single cell layer.
  • Fluids may need centrifuging - thoracic or abdominal effusions can be collected using a 21G catheter. By concentrating the sample using a centrifuge you’ll reduce cell trauma. Ideally make slides of both the fluid sample as collected and a sample of centrifuged fluid sediment. For effusions with a high cell content, a direct smear may provide a representative sample of cells for analysis.

2. Non-aspiration fine needle procedure:

This technique also uses a fine 21G – 25G needle, but a syringe is not used. The needle is inserted into the tissue and redirected within the mass at several different angles. This technique works well for most samples. Indeed it may be more effective than the FNA technique when sampling from highly vascular areas. Once the needle is withdrawn, attach it to an air filled 5ml syringe and gently expel the needle contents onto clean glass slide as described above for the FNA’s.

3. Impression smears:

These are effective for erosive lesions. If crusts are present, remove them first to expose the surface exudate. Unfortunately they can sometimes be of limited value because we only collect the surface inflammatory exudate and not the deeper cells.

4. Scrapings:

Use a No10 scalpel blade to gently scrape across a lesion to collect a representative sample of cells. The technique is used for oily scale, lichenification, ulceration and skin lesions.

5. Cotton swab smears:

These are effective when samples from skin, ear or conjunctival lesions are required. They are commonly used when diagnosing otitis and pustular dermatitis. Unless the location is very moist, lightly moistening the swab with 1 or 2 drops of sterile saline prior to collection to minimise cell damage. Smears are prepared by gently rolling the swab over a glass slide. Do not smear the swab on the slide in a side-to-side motion as this causes cell rupture.

6. Adhesive tape:

This technique is used to sample areas that are hard to access using a direct impression smear technique. Transparent acetate tape is applied to dry lesions that will not stick to a glass slides easily (e.g. skin). The middle of the sticky side of the tape is pressed firmly against the lesion several times to pick up cells before attaching to a slide and then staining and examining.