Pathology

Pathology Submission Guidelines

Submission of tissue specimen(s) is often the best method of obtaining a diagnosis. However, proper selection and preservation of samples is essential to make the most efficient and economical use of the laboratory. The two conditions that most frequently interfere with diagnosis are (1) post mortem autolysis, and (2) sample collection too late in the course of disease.

Fresh specimens should be large enough to demonstrate the lesion yet small enough to allow for rapid chilling. In some cases (e.g., bronchoalveolarlavage for PRRS virus isolation) submission of an entire organ may be preferred. Ideally, fresh samples should be packaged individually to prevent cross-contamination. It is absolutely vital NOT to package fresh intestine with other tissues, as this results in fecal contamination of other organs. At a minimum, intestinal samples should be submitted separate from all other tissues. Samples should be shipped in leak-proof containers with artificial freeze packs. Please line shipping containers with additional sealed plastic bags to avoid leakage in transit. A fee of $25 may be assessed for packages that leak. Specimens for histopathology should include slices of the appropriate organs, including the lesion, transitional zones, and adjacent grossly normal tissue, in 10% buffered formalin in a leak-proof, wide-mouthed solid container. DO NOT USE GLASS CONTAINERS. When in doubt, collect specimens from multiple organs, including brain. The pathologist can then select the most appropriate specimens for complete microscopic examination. Unless it is important that individual animals be examined and reported separately, specimens from each individual animal can be pooled in a single container - provided the specimens are small enough to maintain a 10:1 formalin:tissue ratio. The ratio of formalin:tissue must be at least 10:1 to allow adequate fixation.

A minimum of 48 hours is required for histopathology, 24 hours for fixation and 24 hours for processing. Consequently, specimens for histopathological examination should be collected and placed in formalin at the time of necropsy in order to minimize autolysis and generally allow results to be available the day after the specimen is received.

General guidelines for histopathologic examination/submission of formalin-fixed specimens are as follows:

Solid organs: 0.5 - 1 cm slices to include lesion and transitional areas between lesions and normal tissue.

Intestine: 1 - 2 cm lengths held open as they are immersed in formalin or flushed with formalin prior to immersion. Do NOT tie the ends.
Brain (including brain stem): immerse sagittal half of small brain in formalin. One-half of the brain should also be submitted from larger animals. These larger brains should be sliced for better fixation. The preferred procedure is to make transverse slices, 1.0 - 1.5 cm apart that extend to within 1.0 cm of the ventrum of the brain. This allows for more rapid fixation while retaining the architecture of the brain so that specific areas can be sampled. Nerves can be pinned to a tongue depressor and immersed in formalin.

Tumors: immerse in 10% formalin. If greater than 1 cm, incise, leaving a base attachment intact.

Impression smears and needle aspirates of tumors are helpful in a few situations. However, actual biopsies are usually required for definitive diagnosis. Stain and examine smears and aspirates in your practice laboratory and, if a diagnosis is not obvious (i.e., mastocytoma, abscess, etc.), biopsy the mass and forward both the biopsy and the smears to the reference laboratory.