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Fine-needle Aspiration: |
| Using a 21- to 25-gauge needle attached to a 5- or 10-mL syringe, the needle should be inserted into the area to be sampled and repeatedly redirected within the lesion while gentle suction is applied. The resulting sample is often very small and may only be present within the needle, not the syringe. The syringe should be detached, filled with air, re-attached, and gently depressed to express the sample onto a clean, dry, glass slide. The force applied should be minimal in
order to avoid rupture of the cells. Another slide is placed on the top of the sample and pulled lengthwise to spread the sample to a single layer if possible. |
| If blood is collected in the syringe during aspiration, this can be centrifuged and the buffy coat examined for nonblood cells. If the sample is directly smeared onto a slide, a feathered edge should be obtained because this is where the heavier cells will congregate. Blood contamination can be minimized by use of a very fine (25-gauge) needle; this increases the chance of collecting diagnostic cells. |
| Lymphocytes are particularly fragile, and aspirates of lymph nodes should be made using a needle only with no attached syringe and no suction. The needle should be repeatedly redirected to pack the lumen of the needle with cells; a syringe is then attached in order to carefully express the sample material. |
| The sample should be air dried as quickly as possible to reduce the effects of shrinkage but should never be heated. |
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Impression Smears: |
| These are often used for ulcerated surface lesions. They usually only sample the surface inflammatory exudate, rather than deeper tissues, and are of limited value. This technique can also be used on biopsies to give an immediate indication of the type of lesion before sending the sample for histopathologic interpretation. The cut surface of the sample is blotted to remove surface blood and serum, then the dried surface is applied to a clean, dry slide with gentle pressure.
Several areas can be prepared on a single slide. The preparations are quickly air dried and then stained as for a fluid sample. |
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Fluids: |
| When a fluid sample is obtained, centrifugation of the preparation and sampling of the centrifuged sediment is the usual method of cell concentration. Once the slide has been prepared, rapid air drying before staining is necessary. |
| If the fluid will be sent to a laboratory, adding a few drops of formalin to the sample will preserve cells and prevent bacterial overgrowth during transit. This is particularly useful for bronchoalveolar lavage fluid and urine because these often contain infectious agents and are prone to bacterial contamination at sampling. The laboratory must, however, be told of the presence of formalin because the usual Romanowsky stains
cannot then be used. Calcium disodium adetate is often recommended to help preserve cytology samples but its effects are limited. |
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