This document describes various smear preparation techniques used in cytology, including direct smears, blood smear technique, squash technique, large volume centrifugation, small volume centrifugation, membrane filtration, cell blocks, density gradient centrifugation, and gravity sedimentation. Direct smears involve spreading the specimen directly onto a slide. Blood smear technique produces a thin, uniform smear for staining. Squash technique results in a thin, uniform preparation. Large volume centrifugation concentrates fluid specimens by separating the buffy coat layer. Small volume centrifugation uses a cyto-centrifuge to deposit cells directly onto a slide. Membrane filtration uses a filter to collect cells on a slide. Cell blocks allow processing samples as histopath

1. Smear preparation techniques
 Direct smear
 Large volume centrifugation
 Small volume centrifugation
 Membrane filtration
 Cell block
 Density gradient centrifugation
 Gravity sedimentation
Direct smear:
A cytological smear made by spreading the specimen directly onto a
glass slide.Direct smears are the simplest and most straightforward of
the several ways to transfer cells from a raw specimen to a slide.
Blood smear technique
 Place a small drop of deposit near one end of glass slide.
 Touch a second slide to a front edge of the drop
 Push the second slide across the surface of first slide.
 The final preparation is thin and uniform.
 The technique is useful for producing thin air dried smear for
Romanowsky type stain.
Squash technique:
 Place a drop of cell deposit near the center of glass slide
 Squash a second slide against the first slide, ensuring slight
overlap.
 Pull the second slide over the first slide, ensuring the two slides
maintain contact and remain parallel.
 The final preparation is thin and uniform, but should not be so
thin as to rapidly air dry.
Note: if the sample is hemorrhagic fishtail smear is suggested.

2. Large volume centrifugation:
Concentration of fluid specimen has been traditionally achieved by
large volume centrifugation. Following the centrifugation of fluid the
objective is to select buffy coat for smear preparation. The buffy coat
layer is the fraction of centrifuged fluid that contains white blood cells
and tumor cells if present.
Small volume centrifugation:
Low volume specimen (˂0.5ml) that fails to yield sufficient buffy layer
for a smear can be processed by cyto-centrifugation. A cyto-centrifuge
is a device that uses centrifugal force to spin cell in a fluid suspension
directly onto a glass slide. This avoid need to make a smear from a
deposit.
Principle:
A cytocentrifuge funnel, absorbant paper and glass slide are clamped
together. A small volume of cell suspension is added to the funnel and
whole apparatus is centrifuged. The final preparation is a small circular
deposit of cell on the glass slide.
Membrane filtration:
 Membrane filtration specially manufactured filter paper
containing microscopic pore through which fluid sample can be
drawn.
 The sample first undergo dispersion step to break up large group
of cells and unwanted debris and is then thoroughly mixed.
 A negative pressure then draws the sample through the filter. The
average size of pore is such that fluid small cell and debris pass
readily through the filter.
 Large cell including tumor cell if present collect on the filter in a
thin even layer.

3.  The layer of is then transferred to a microscopic slide.
Cell blocks preparation:
A cell block is a way of processing a cytology sample as histo-
pathological specimen.Cell blocks prepared from residual tissue
fluids and fine-needle aspirations can be useful for establishing
a more definitive cytopathologicdiagnosis.
Thrombin-Clot Technique:
A cell block can be prepared from the pellet of any centrifuged cells
suspension by embedding it in a clot formed by added plasma and
thrombin. The clot is then added to a pot of formalin and processed as
histopathological specimen.
Density gradient centrifugation:
 In this technique a measured aliquot of sample is carefully
dispensed on the top of a density gradient fluid in a centrifuge
tube.
 A density gradient fluid is concentrated sugar solution is added to
specimen and centrifuged, different cell types are separated into
layer according to specific gravity.
Gravity sedimentation:
A settling chamber is clamped to a glass slide and cell suspension is
added. Sufficient time is allowed for cell to settle on the slide under
gravity. Slide may be electrically or coated with suitable material to
facilitate cell adhesion. Albumin and poly-l-lysin are commonly used
adhesive.