- Sample the lesion and describe its gross appearance and extent (size or % of organ affected).
- Maximum sample width = 8mm (except for brain – see below).
- Fixation of 8mm slices takes about 24 hours:
- large sections delay fixing, promote autolysis and decrease formalin volume
- the largest tissue section on a slide is 20x30mm so larger specimens are wasted
- Consider multiple sections if multiple or large lesions need examination.
- Ensure samples are representative of lesions. For large lesions:
- sample the interface with normal tissue and
- areas of different colour or consistency.
- Ensure samples are representative of tissue (some organs have different functional areas):
- kidney has cortex, medulla and pelvis; heart has left and right ventricles, inter-ventricular septum, valves, atria etc.
- Cover multiple diagnostic options (gains background data for your client’s properties).
Fixing samples in formalin
- Use 10 times as much 10% buffered formalin as tissue.
- Warming increases fixation rate – and fumes. Ventilate area well and seal jars.
- Fixed tissues expand. Avoid narrow-necked jars as tissue cannot always be safely removed.
- Fixed tissues can be drained before transporting to the laboratory. Seal well and add a few millilitres of formalin to moisten tissue.
- For transport, pool fixed tissues in reduced volumes of 10% buffered formalin unless samples cannot be distinguished from one another or are diagnostically relevant (e.g. multiple lymph nodes from different sites need to be individually identified).
- Remove the whole brain – different sites are examined for different diseases. See the Brain removal techniques guide.
- Use swabs of the brain and/or meninges or a small section of frontal lobe/cervical spine for culture, then fix the whole brain. The brain fixes whole but takes 3–4 days.
- Rabies and organophosphate testing need fresh, chilled, half a sagittally sectioned brain.
- Hepatic blood flow is not homogeneous. If no gross lesion, sample left and right lobes.
- Pulmonary air flow is not homogeneous. If no gross lesion, sample cranio-ventral and dorso-caudal areas.
- Intestinal sections should be 25mm long, unopened with a 5mm nick in each end to allow optimal formalin penetration without damaging mucosal surfaces.
- Do not scrape, wipe or mush mucosal surfaces and tissues that you want examined
- Sample multiple muscles for nutritional myopathy. Most consistently affected are semitendinosous, semimembranous and lateral and medial vastus.
- If sending whole or live animals, call the DPIRD Diagnostic Laboratory Services (DDLS) pathologist before submission.
- DPIRD Diagnostic Laboratory Services – Animal Pathology: DDLS@dpird.wa.gov.au or duty pathologist +61 (0)8 9368 3351
- Your local Department vet: see Livestock Biosecurity veterinary contacts
- Other guides to assist veterinarians in conducting post-mortems: Veterinary sampling and post-mortem resources page
- After hours emergency animal disease hotline: 1800 675 888