Fine Needle Smear Preservation

There are several methods for smear preparation. There is no scientific evidence to suggest one technique is better over another, often the choice is down to personal preference. Usefulness can depend on preference and the content/viscosity of the sample. These include ..

• The squash technique - most effective

• Push/pull technique - most effective

• Line concentration technique

• Star

• Twist

When producing a smear what much be produced?

A monolayer to allow the slide to be appropriately examined

To avoid degradation of cells, the collected sample should be ..

Rapidly transferred from the needle to a microscope slide

A delay in transfer from the needle to the slide can lead to ..

Clotting within the needle shaft, trapping the sample in the needle shaft

Placing the sample onto the slide

Rest the needle, bevel down, onto the labelled slide and depress the plunger briskly, resulting in a droplet on the slide

Squash technique

• Simple and often preferred method

• Excellent for semisolid, mucoid and viscous materials and small volume samples

• The sample is expelled from the needle, in the middle of the slide

• A second slide is placed at right angles to the first slide, on top of the sample, with an overlap either side

• Second slide is then pulled along the lower slide, spreading the sample

• Contact must be maintained, and the slides must be parallel to one another

• Downwards pressure should be avoided to prevent cell damage

Push/pull technique

• This technique is slower than other, more preferred techniques

• Cell degradation due to desiccation of the sample

• Used for samples with suspected low cellularity e.g. fluid washes

Line concentration technique

• Excellent for semisolid material and small volume samples

• Used for samples with suspected low cellularity, e.g. fluid washes

• Same technique as push/pull but spreader slide lifted from the sample slide when approx. 2/3rd along the slide

• The end line formed by using this technique will contain a concentrated quantity of cells

• Can cause damage and lysis of cells due to shearing action of the slide

Star technique

• The sample is placed in the centre of the slide, and the aspirate needle is used to drag the material into radiating streaks from the central droplet

• Minimally traumatic to cells but is a relatively ineffective method of spreading the sample thinly

• Often too thick for examination, but can be used for samples with suspected low cellularity, e.g. fluid washes

Twisting technique

• The sample is expelled in the middle of the slide. A second slide is applied over the sample and the slides are twisted at 90 degrees counter to each other before being lifted off

• The slides stick together which can cause cell damage

• Smear is often too thick to assess, but can be used for samples with suspected low cellularity, e.g. fluid washes

Smears should be rapidly air dried to avoid ..

Shrinking of cells (drying artefact)

When transferring to the slide, keep the sample in a single droplet form, this is to avoid ..

The sample drying out before smearing is possible

Why is it best to use pencil when labeling the slide as opposed to pen?

Ink may be washed off during staining whereas pencil won’t

Ensure smears are thin and no blood is present within the sample, this will allow ..

Full visualisation of cells within the sample

Do not apply pressure to the sample as this will ..

Damage the cells

Ensure the sample is central and away from slide edges - why?

May not stain effectively, finger contamination, difficult to access under microscope

DO NOT exposure smear slides to formalin (including fumes), when shipping the smear should be ..

Packaged separately if shipping other samples preserved in formalin to prevent exposure of the slide

Slide preparation tips

• Transfers and make the smear as quickly as possible

• Minimise handling of slide and ensure it is clean prior to sample preparation

• Label slide with patient ID and date

• Prepare at least two slides from each sample collection

• Repeated sample and sample preparation is recommended if poor initial exfoliation or sample preparation

RVN roles

Sampling techniques that enter a body cavity cannot be performed by an RVN/SVN - All these procedures are outside the remit of schedule 3

Most, but not all, fluid samples harvested will be prepared and preserved in a similar way ..

Using a sterile EDTA tube and plain blood tube - to inhibit bacterial growth and reduce cell lysis

Fresh smears can be a useful cell preservation technique, but this should not be used for CSF cells, due to ..

The fragility of cells