Common cytology sampling errors

Cytology sample collection

Choose the method – FNA vs impression smear

• Both methods are good, but they are not the same! Clinician has to decide what questions to ask and what will be helpful.
• FNA – gives information about deeper tissues. This is a technique of choice if a mass is present/neoplasia is suspected.
• Impression smear – superficial material, frequently contains less informative material – secondary inflammation, cells from the skin surface etc. Good choice for seeing superficial pathology – infectious agents (malasezia, chailitiella etc).

Cytology sample collection

Aspiration vs Non-aspiration (capillary technique)

• Aspiration

– usually yields more cells

– better for poorly exfoliating masses (harder on palpation, lipomas)

– more traumatic to cells

– blood contamination more common

– be careful not to apply too much negative pressure in the syringe (~ 1cc is enough), move the plunger once and redirect the needle, repeat at least 4x

– always release negative pressure before the needle is taken out of the mass. This is important!

– once needle is out of the mass it is separated from the syringe

– 1 cc air is drawn in the syringe, needle is reattached and material is expelled on the slide

• Non-aspiration

– better for fragile cells (lymph nodes, endocrine tissues)

– can be performed with the needle only (syringe not attached)

Cytology sample collection

Redirect the needle

– Regardless if you aspirate or use non aspiration technique (capillary technique) – needle redirection is essential

– Redirection is movement of the needle/needle and syringe back and forth without taking it out of the mass

– Minimum 4 redirections are needed

Cytology sample collection

Needle size

– 22-25G needles are most commonly used. But every time after the palpation of the mass veterinarian has to choose the needle for that particular mass. The firmer/harder the mass – larger the needle (22G), softer mass – smaller needle diameter (23-25G).

– 22G needles can produce the core sample that is difficult to put on the slide in monolayer.

Slide preparation

– In my experience gentle rolling with the side (not the tip) of the needle you just used to obtain the aspirate is the best option

– Squash prep – squash the material between two slides is classically described in the text books, I find that this frequently causes too much pressure on the cells and they break

– Other methods can be used for liquid materials – more on sample preparation in the future.