Cytology – an essential veterinary tool

There is so much that can be achieved using cytology in veterinary practice. It’s used almost every day throughout the world providing pathological answers with the minimum of expense, effort and time. By collecting and preparing the best possible sample we can use the information to make a diagnosis, consider differentials and prepare a treatment plan.

Posted: 07 March 2018

Cytology – an essential veterinary tool


Why is cytology so useful?

There is so much information that can be collected and analysed with minimal fuss in minutes. It’s also cost effective so most clients should be able to afford the work.

By identifying the cell population we can make a variety of clinical judgments about the cells. For example we can ask if the cells are;

  • Inflammatory – and if the sample represent acute or chronic inflammation.
  • Infected – by looking for bacteria we can determine if there is any evidence of infectious organisms.
  • Hyperplastic, reactive or normal – helpful when trying to determine if cells have altered in response to antigens or to disease.
  • Neoplastic – cancerous cells can be easily identified. The degree of malignancy can also be predicted.
  • From a transudate or an exudate – a transudate results from an imbalance in oncotic and hydrostatic pressures whereas an exudate is the result of inflammation and often requires more extensive evaluation and treatment.

What are the advantages of cytology over histology?

[Insert image of cells as viewed under oil immersion]

When presented with a case requiring pathological analysis, a decision needs to be made regarding how best to obtain and examine samples. In many cases histology may be preferred, but in an equal number of cases, cytology is more effective. Some of the main advantages of cytology over histology are;

  • Pre-operative samples – if an excisional biopsy is anticipated, by collecting pre-operative samples you can plan the extent of surgery and technique required.
  • Minimal invasion – the technique is simple, relatively painless and often requires no anaesthesia or sedation
  • Cost effective – the collection and analysis of samples can be performed in many cases in-house. Even if the samples are sent to an external laboratory, the overall cost is minimal compared to collecting a full biopsy for histology.
  • Rapid recovery – for most cases, anaesthesia is not required and animals are usually free to go home immediately.
  • Rapid results – often within minutes of collection if performed in-house.
  • Neoplasia monitoring – useful as a simple technique for collecting and monitoring regional lymph nodes for recurrence of neoplasia.
  • Microorganisms can be cultured – samples don’t need to be fixed in formalin so culture from aspirates is possible.

What do you need for cytology?

All the items are readily available in all veterinary practices, so there really is no excuse.

  • Needles – 21G or 25G needles are ideal
  • Syringes – a 5ml disposable and sterile syringe
  • Cotton swabs – sterile swabs for rolling across tissue
  • Scalpel blades – a ‘scrape’ across the tissue to collect cells
  • Glass slides – frosted end to allow labeling
  • Differential stain – many practices use Diff-Quik®
  • Microscope with oil immersion lens – this is where it’s worth investing in the best equipment your practice can afford. Quality microscopes with good lighting and optics are a pleasure to work with.

13 ways to improving your cytology

[Insert image of a vet performing a Fine Needle Aspirate on a dog]

  1. Stabilise the tissue – if the mass or tissue being aspirated can be palpated, it helps to hold it firmly in one hand whilst aspirating using the other.
  2. Use sedation – if the animal is difficult to handle it may require sedation. Pre-anesthetic agents including sedatives and/or analgesics will all help to keep the animal calm and still whilst collecting your samples. If additional restraint is required, short safe anaesthesia can be achieved using isofluorane/sevofluorane. Many small mammals with body cavity effusions are depressed and manual restraint may be adequate.
  3. Use analgesia - local anaesthetics (e.g. Lidocaine 2%) may also be injected into the area close to where you plan to collect the FNA, whilst being careful to avoid contamination of the sample site itself.
  4. Keep it clean – stains that become dirty or contaminated should be filtered or cleaned regularly. It may help to use one set off stains for obviously contaminated specimens and another for clean samples such as effusions and fine needle aspirates. Filter the stain twice weekly to help remove hair, wax, bacteria and other obvious contaminants.
  5. Replenish stains regularly - change stain completely on a monthly basis.
  6. Dry the slide carefully – use a hair dryer on the low to medium heat setting for quick drying of slide specimens.
  7. Use of the microscope – keep the light condenser up when examining a cytology sample. An oil immersion field is usually necessary for detailed cytological interpretation. Cytological preparations should first be scanned under low power for an area of evenly distributed cells, one layer thick.
  8. Keep and review old slides – diagnostic slides from interesting cases can be reviewed at a later date especially after your receive a pathology report.
  9. Use the correct technique - avoid aspirating too aggressively when collecting a fine needle sample. This will help prevent cell trauma and excessive bleeding. Likewise, handle the slides with care when preparing the sample.
  10. Be aware of bacteria – if they are within the cell they are probably pathological. Bacteria outside the cell could be from contamination.
  11. Avoid blood contamination - use the non-aspiration needle biopsy technique for vascular lesions.
  12. Be quick – don’t take too long collecting and preparing your samples. Make smears immediately after collection to optimise cell preservation.
  13. Multiple samples - collect 2-3 separate preparations, especially if the mass/lesion is of sufficient size.