CPD ACCREDITED ARTICLE
3. Scrapings
Scrapings could be useful for obtaining cells from
firm surfaces, such as firm cutaneous lesions. Cells
obtained by means of a scalpel blade are gently
smeared onto a clean glass slide. This often gives
many broken cells, but areas of intact cells can
usually be found.
4. Swabs
Swabs can be used to obtain cells from mucosal
surfaces such as the rectum or vagina, or in areas
where the other sampling methods are not practical,
such as fistulous tracts. The swab must be gently
rolled along the surface of a clean glass slide.
Preparation of slides
Once a sample has been collected, it needs to be
transferred to a clean glass slide and spread out -
the aim is to obtain a monolayer of cells. This needs
to be done quickly before the material dries out or
clots. There are various techniques, depending on the
volume and consistency of collected material.
1. Solid tissue aspirates
• Slide over slide (“squash”) preparation
This is generally the best method for preparing
slides, if done properly but does need some practice.
The material collected is placed in the middle of a
clean glass slide (the smear slide). A second slide
(the spreader slide) is placed over the sample,
perpendicular or parallel to the smear slide. The
weight of the spreader slide will cause the sample
to spread. Once this has happened, the spreader is
gently drawn across the smear slide, without any
downward pressure, as this will rupture cells. (Fig 3)
The weight of the second slide is enough to cause
the cells to spread. Non-fragile tissues (e.g. from
carcinomas) or any thick viscous material (such as
mucous strands from trans-tracheal aspirates) can
be spread by this method. With some experience,
and a gentle touch, this method can also be used for
more fragile tissues like lymph node or spleen.
Fig 3: Slide over slide (“squash”) preparation
Fig 4: Blood smear technique
• Blood smear technique
This is done in a similar manner to making a blood
smear. The material is placed near the end of a
smear slide. The spreader slide is placed in front of
the material at a 45-degree angle, backed up until
the material is touched and then moved forward. (Fig
4) The feathered edge should not be right on the
edge of the slide, as the stage retaining clamps on
the microscope will interfere with the oil immersion
lens and the sample then cannot be viewed.
Malignant cells are often found in the feathered edge.
This technique works well for tissues with a fluid
component, like internal organs and lymph nodes.
• “Starfish” preparation
Here the tip of a needle is used to drag the material
in several different directions. It is a gentle technique
that does not cause much rupture of the cells, but it
does leave a thick layer of tissue fluid around the cells
that may stop them from spreading to an acceptable
shape and size.(Fig 5) Usually some areas that can be
interpreted are found. This is not a commonly used
or preferred technique (rather try a squash prep),
but can be used when grainy or viscous material is
aspirated.
Fig 5: “Starfish” preparation
Issue 01 | MARCH 2018 | 27