Texas Equine Veterinary Association

www.texasequineva.com • 20 tissue samples for histopathology and other diagnostic tests. TVMDL also routinely performs necropsy on full animals. In either scenario, it is imperative that necropsy is performed as soon as possible after death so that postmortem autolysis is reduced. For a large animal, necropsy should ideally be performed within 24 hours. Autolysis is unfortunately a common enemy that can hinder both gross and histologic examination. Autolysis is more common in large animals, as it takes longer for their large, deep body cavities to cool after death. Furthermore, the high heats of Texas rapidly accelerate autolysis and decomposition, especially in the summer. In addition to a typical clinical history including clinical signs, duration of illness, number of animals affected, etc., the necropsy history should include the approximate time of death. If performing their own field necropsy, practitioners should include a description of their necropsy findings along with the clinical history. Even if no obvious abnormalities were identified, it is still useful for the pathologists to know that information. Practitioners are encouraged to take pictures of any suspicious lesions they encounter during necropsy and submit them to the laboratory, as they can be helpful for the pathologists. Sections of all organs should be collected during necropsy, both normal and abnormal. Any lesions should be targeted with multiple sections collected. Culture swabs of certain lesions may be indicated. In horses, both stomach and cecal contents should be collected, as they may be needed for toxicology testing (see toxicology section for more information). Submission of a variety of fresh tissue samples to the diagnostic laboratory is recommended following field necropsy. This ensures that adequate samples are available should further testing be needed. For example, histopathology may identify a need for PCR or other tests. If a practitioner needs guidance on what tests to request based on the necropsy lesions and/or clinical signs, they are encouraged to call the laboratory to speak with a diagnostician or pathologist for consultation. Fresh (non-fixed) tissue samples should be stored and shipped chilled. Gastrointestinal samples should be sent in separate containers from other fresh tissues to avoid contamination. Zip lock type freezer bags can be used for fresh tissues. If postmortem tissues will be submitted for histopathology, they should ideally be placed into formalin as soon as possible to limit further autolysis. Organ samples should be sectioned into ~1 cm thick sections to allow for proper fixation, which is the approximate thickness of a starburst candy. This rule is especially important for more dense and bloody organs such as the liver, spleen, and kidney. It is common for TVMDL to receive large, thick sections of these organs in formalin which are not adequately fixed in the center. Additionally, tissues should be placed in ample formalin with at least a 5:1 ratio. Insufficient formalin can result in incomplete fixation. Fresh tissue samples can be and often are submitted to TVMDL with a request for histopathology. These samples can be placed into formalin at the laboratory, for a small processing fee; however, there is a risk that these samples may have increased levels of autolysis due to the interval between collection and formalin fixation. Q: What are the sample requirements and how do I get the best results with clinical pathology test requests (equine focus)? CBC The required specimen is 1mL non-clotted whole blood in EDTA. For best results, provide 1-2 freshly prepared blood smears, air-dried, and unstained. Protect the blood smear from cold (i.e. refrigerator and ice pack), which can distort blood cells. See our website for instructions on how to make a blood smear. Ensure the EDTA is filled to an appropriate level. Under filling EDTA tubes can cause crenation of RBCs and affects values in the CBC. Clinical Chemistry The required specimen for clinical chemistry requests is 0.5 mL serum or lithium heparin plasma. For best results, whole blood should be centrifuged within 1-2 hours of collection. Serum or plasma should be removed from cells and placed in a non-additive tube. Cytology – Fine Needle Aspirates For cytology (fine needle aspirates, Markedly decreased glucose is often an artifact of delayed separation. Many other analytes can be affected by delayed separation and the hemolysis that results from delayed separation. WBCs cannot be identified when whole blood has been stored for too long or reached high temperatures. Marked septic neutrophilic inflammation (diplococci bacteria) in joint fluid from a foal.

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