Problem: Poor cell preservation of cytology samples
Several excellent veterinary textbooks address collection and preparation of cytologic specimens in detail (see the suggested
reading list below). Additionally, taking the following steps will increase the likelihood of obtaining a high-quality specimen
by maintaining cell preservation.
1. Avoid using small-gauge needles (< 25 ga), as cells may be destroyed during aspiration or when they are expelled from
the needle onto the slide. (Note: Some pathologists discourage use of 25-ga needles, whereas others think these are acceptable for obtaining diagnostic
Once material is expelled onto the slide, it should promptly be prepared for staining. This is important to avoid thick or
clotted specimens, which are often nondiagnostic (Figure 2). A popular slide preparation technique is the squash prep, or slide-over-slide, technique (see The squash prep, or slide-over-slide, technique). The sample is expelled onto a clean slide near one end, preferably toward the frosted edge. A second slide is gently placed
flat onto the sample at a right angle, forming a cross-shape when viewed from above. A smooth horizontal motion is used to
spread the material along the slide. It is important to note that the weight of the spreader slide is sufficient for this
technique, and that any additional digital pressure on the slides will increase the likelihood of cell rupture.
2. A lymph node aspirate from a dog. Note the ill-defined cells with pale-pink nuclei. The slide was improperly prepared,
resulting in a thick, poorly stained specimen (Wright's stain, 20X objective). (Photo courtesy of Dr. Rebeccah Urbiztondo.)
Slides can also be prepared for staining by using the same technique used for blood smears. The blood smear technique is often
useful for cystic or fluctuant lesions or body cavity effusions.
Yet another option for slide preparation is the starfish technique. This technique is performed by carefully dragging a needle
through the sample to create multiple thin strips of material radiating away from the center. The starfish technique can be
particularly useful if cell rupture is a recurring problem when using the squash prep technique.
If impression smears are being made (e.g. from a surgical biopsy), it is often useful to lightly blot the tissue sample with gauze or absorbent paper to remove excess
blood. The surface of interest is then lightly touched to the slide several times, creating a row of imprints. Excessive force
or smearing of the tissue should be avoided to minimize cell rupture.
2. Do not place unstained slides in a refrigerator or freezer, and always allow slides to air-dry before placing them in
containers or bags for shipping. A hairdryer can be used to expedite this process, but the slides should be monitored to avoid prolonged exposure to heat.
Unstained slides that are refrigerated or are packed for shipping before fully drying may have an artifact that severely distorts
3. A splenic aspirate from a dog. This slide was exposed to formalin, resulting in severe artifact. Note the dark-blue discoloration
(Wright's stain, 10X objective). (Photo courtesy of Dr. Rebeccah Urbiztondo.)
3. Never allow specimens collected for cytologic evaluation to come into contact with formalin or formalin fumes. Such contact also results in severe artifact and often renders the sample nondiagnostic (Figure 3). This is a potential complication when unstained slides and biopsy samples are shipped in the same package.
4. Be particularly careful with lymph node aspirates, one of the most common samples affected by poor cell preservation because
of the fragility of the cells. The sewing machine technique is often successful in obtaining high-quality samples from lymph nodes (Figure 4). If multiple lymph nodes are enlarged, the practitioner should aspirate several nodes to increase the likelihood of obtaining
diagnostic samples. Each slide should then be properly labeled to indicate which lymph node was sampled. Some laboratories
consider multiple lymph nodes as a single site and will charge accordingly, although the practitioner should verify the policy
of the laboratory before submission to avoid unexpected charges for additional sites.
4. A lymph node aspirate from a dog. This slide was properly prepared and stained. Several mast cells are present with considerable
variation in size, nuclear:cytoplasmic ratio, and degree of granulation. This sample was diagnostic for metastatic mast cell
neoplasia (Wright's stain, 100X objective). (Photo courtesy of Dr. Rebeccah Urbiztondo.)