Chapter 5 - Sampling and Testing
5.6 Histopathology

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5.6.1 Introduction

Histopathological examination can provide considerable information about disease processes that cannot be inferred solely by gross examination. Reasons that a veterinarian should submit samples for histology include:

  • to confirm the accuracy of a diagnosis which has been made on the basis of gross pathology;
  • to confirm or rule out a condition suspected on gross examination;
  • to identify a condition which is unfamiliar to the referring veterinarian. Besides allowing the veterinarian to determine the disposition of the carcass and offal, this may lead to the discovery of a previously unrecognized condition;
  • to determine the extent of a condition, for the purpose of making a disposition, such as by identifying the invasiveness of a neoplasm, or the presence of metastasis.

5.6.2 Sample selection

Any carcass in which the diagnosis is uncertain should be sampled. In addition, veterinarians should occasionally submit samples of conditions for which they are certain of their gross diagnosis, to ensure that their diagnosis is correct. Unusual conditions may sometimes resemble familiar ones.

Samples must be representative of the condition; if multiple lesions are present, and appear to represent various stages in progression, then early, middle, and late stages should be sampled.

Sample multiple tissues. Organs which appear grossly normal may still show histological changes which will affect the diagnosis. The selection of appropriate organs to sample will, of course, be based on the veterinarian's knowledge of the pathogenesis of the disease or diseases suspected.

Include the edges of lesions. If a lesion is large, both the edge and centre should be sampled.

5.6.3 Testing

Samples from the Western Area should be sent to the Lethbridge Laboratory. Samples from Ontario, Quebec, and Atlantic Areas should be sent to the St. Hyacinthe Laboratory (Laboratoire d'Hygiène Vétérinaire).

Samples should be submitted in 10% formalin. The volume of formalin should be 10 to 20 times the volume of tissue. Specimens should be no more than 1 cm thick, in order to ensure adequate penetration of the fixative. The specimens should be fixed for at least 24 hours prior to processing; however, the time required for the sample to reach the lab will usually take care of this requirement.

The submission should be accompanied by form CFIA/ACIA 5439 Disease Control Specimen Submission, which is available on the LSTS Sample Submission Form application. An adequate description of the gross pathology must be provided in the block marked "Submission comments/history". Ensure that the "submitter" block is fully completed, including a telephone number at which the submitter can be contacted in the event that the pathologist requires additional information. If applicable, an email address should also be included. If the submitter's name is entered in the electronic version while on line, this information will be completed automatically; make sure it is correct and legible.

If the carcass has been held pending histopathology, record the held tag number in the space marked "Sample/vial no.", and include the phrase "Carcass Held" at the start of the "Submission comments/history" block. Ship the samples for overnight delivery. The submitting inspector should inform the operator of the expected time period before results are available; this would normally be 10 working days.

If the carcass is held, it is the responsibility of the operator to determine the necessary steps to maintain the integrity of the meat product. This might include boning, packaging, refrigeration, or freezing. As with any held product, the operator must request permission, and these measures must take place under CFIA supervision. Alternatively, the operator may request permission to treat the product as inedible and dispose of it.

5.6.4 Follow-up

If the condition suspected is such that the outcome of the histopathology could affect the disposition, then the carcass and offal must be detained pending the result, or discarded. Results can usually be obtained within 5 working days of the time of shipment. Additional time may be required for specimens which are mineralized or require special stains to make a diagnosis.

See Chapter 17, Section 17.9, for guidance on carcass disposition.

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