As of October 31, 21016, a new tissue processing method has been implemented at the Veterinary Diagnostic Laboratory, using stainless steel ball bearings in an automated mechanical disruption machine. As a result of our comparison studies (with our previously used tissue processing method), testing for swine Influenza A Virus (IAV) does not require a lung-only sample. Tissue homogenate, which includes lung and other organs, is acceptable and appropriate for IAV testing since no statistical difference was seen in IAV real time PCR and virus isolation results in 33 paired samples of lung-only and tissue homogenates
- Commercial Formaldehyde (37-40%) - 100 ml
- Distilled water - 900 ml
- Sodium phosphate monobasic - 4.0 g
- Sodium phosphate dibasic (anhydrous) - 6.5 g (pH should be 7.2 ± 0.5)
Ten percent neutral buffered formalin is the fixative of choice.
- Place in fixative as soon as possible.
- Fix tissue slices 24-48 hours. Tissue volume should be less than 1/10th that of the formalin solution. Slices should be no thicker than 1 cm. If formalin is not available, the tissues should be refrigerated and shipped cold (frozen gel packs or equivalent). Do not freeze.
- Use wide mouthed, leak proof containers. A tissue that is fresh and pliable can easily be put into a narrow mouthed jar, but it becomes hard when fixed and cannot be readily removed.
- Alternatively, tissues can be fixed in formalin solution for 24 - 48 hours, removed from the solution, wrapped in a formalin-soaked gauze sponge, placed in a plastic bag, and sealed for shipment. This technique decreases the probability of formalin leakage during shipment.
- Special histopathology requests - Some samples, such as eyes, may require different fixation or handling procedures. Please contact the laboratory prior to taking these samples.
Protect formalin - fixed specimens from freezing.
Freezing produces artifacts in tissues that generally result in the sections being unsuitable for interpretation. Protect formalized samples from direct contact with frozen packs OR frozen specimens as this may result in freezing of the fixed tissue. During cold weather it may be necessary to use an insulated container for shipping formalin-fixed specimens.
Samples From a Necropsy
Submit sections of lesions and samples of major organs: lung, heart, liver, kidney, spleen, brain, ileum, endocrine tissues and colon.
Ship fresh unfixed brain in a hard container such as a Tupperware or similar plastic container.
Surgical Pathology Samples
Attention to certain details will help assure that a sample will provide the diagnostic information needed.
- Provide pertinent clinical history, physical examination findings (distribution and duration of the lesions) and clinical laboratory findings. This will help the pathologist interpret the findings in the context of the clinical case and helps to ensure that useful information is obtained. This information is of most critical importance for skin biopsies.
- Provide a precise description of the lesion that was biopsied as well as the site of the biopsy. These features are often critical for proper interpretation of the lesion.
- If the lesion was previously biopsied, the case accession number (if previously sent to the VDL) or previous biopsy report, is often useful in evaluating whether the lesion is the same disease process as in the previous biopsy and whether progression or regression has occurred.
- For excision biopsies in which the completeness of excision margins is evaluated, it is very helpful if the surgical margins are stained by the surgeon with india ink (other inks will dissolve in the solvents used in tissue processing).