Publicidad
Methodology Guidelines
in cytological studies is alcohol. Alcohol produces distinct
nuclear chromatin patterns, and also serves to remove water
from the cells. Cell-Fixx spray fixative is an example of
an alcohol based cytological fixative which also contains
Carbowax.
A disadvantage of alcohol fixatives is that they evaporate
quickly, and therefore there is always the risk of permitting
specimens to dry out. To avoid this, many laboratories
use Saccomanno fixative, which is a mixture of 70% ethyl
alcohol and 2% Carbowax (polyethylene glycol). The
Carbowax in this mixture forms a coating over the specimen,
helping protect from the effects of drying. The Carbowax is
soluble in water, and so is dissolved in subsequent staining
steps. Commercial versions of this fixative are available (for
example Cytospin Collection Fluid).
When specimens must be transported over considerable
distances, or when they cannot be processed immediately,
it is advisable to fix with alcohol or with Saccomanno type
fixative. This is done by adding an equal volume of fixative
to the sample. If the specimen is large in volume, the sample
should be centrifuged to concentrate the cells, and then
fixed. Immediately after adding the fixative to the sample,
the sample should be vigorously agitated to suspend the
sample within the fixative.
Occasionally samples will be received that have been
fixed in some other fixative such as formalin. These will
have a different nuclear and cytoplasmic appearance if
processed without exposure to alcohol. Such specimens
can be concentrated, the formalin poured off, and then
re-suspended in Cytospin Collection Fluid. The result will
be a specimen that is reasonably similar to those fixed in the
alcohol fixative alone.
Fixation makes cells more rigid and less able to spread when
placed in the Cytospin. Specimens that have been fixed prior
to depositing on slides will require slightly higher speeds and
longer times to achieve the same degree of spreading as seen
in unfixed specimens. Occasionally the laboratory will be
asked to prepare specimens that have been held in fixative
A78310250ES 5.1ª Edición
Manual de operaciones de la Cytospin 4
99
Publicidad
