Sampling techniques
The most appropriate sampling technique depends on the site and the gross appearance of the node to be sampled as well as the tests being performed on the sample. For cytologic evaluation of lymph nodes, fine needle aspiration (FNA) or fenestration is performed as described for other solid tissues (see Chapter 1).
As with large masses, aspiration of peripheral areas of the node is preferred, since the center of a large node could be entirely necrotic. Alternatively, impression smears can be prepared following surgical excision of a lymph node and may provide useful diagnostic information due to the extreme rapidity and morphologic details of cytologic impressions. It is recommended that multiple slides are prepared and a subset is stained with a Romanowsky-type stain for microscopic evaluation. Previously stained slides can be used in some immunocytochemistry (ICC) protocols; others require unstained slides. Stained or unstained cytology slides can be submitted for polymerase chain reaction (PCR)-based diagnostics. Samples collected for analysis by flow cytometry should be placed into a suspension medium (e.g. Roswell Park Memorial Institute (RPMI) 1640, phosphate buffered saline, or other physiologic saline solution with the addition of 10% of serum of the same animal). An aliquot of the sample collected into suspension medium can be processed for use in PCR assays or cytocentrifuged at approximately 100 g for 3 minutes for microscopic examination. If microbiology cultures are required, a portion of the sample should be placed into a sterile tube.
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