Vet Lab Manual

Toxicology

It is not possible to comprehensively screen samples for 'poisons' or 'toxins'. It is up to the submitter to consider the history, clinical signs and lesions (if any) and identify specific toxins for analysis. Contact your Regional Veterinary Laboratory if you are unsure whether a test is available for a particular toxin.

In cases of suspected poisoning, it is important that an effect be demonstrated in the animal. For example, nitrate poisoning is confirmed by demonstrating the presence of nitrate in the serum or blood of the animal, not by demonstrating the presence of nitrate in pasture plants in the paddock.

It is important that the history provided includes details of treatment with any suspected toxic compound, particularly in relation to the strength of the preparation and the time since treatment or access to the material.

Standard Containers and Equipment

Blood vacuum tubes, 10 ml

For blood samples

Leakproof 5 ml tubes or bottles

For serum samples.

Bottles and jars

For tissue samples

Slides

These must be clean. Some brands available have not been washed and are not suitable unless they are washed.

Collection of Specimens

Particular care should be taken in collecting and packaging specimens for toxicology, because there is often a possibility that infectious agents are involved and these can create hazards to staff handling the material in a laboratory. Therefore avoid contaminating the outside of any submitted containers with tissues and ensure they are leakproof.

Tissue samples

At least 100 g of tissue should be collected, taking care to avoid contamination with soil, faeces or intestinal contents.

Separate organs should be placed in separate containers.

Body fat is the preferred tissue for insecticide residue testing. For biopsy material, a minimum of 2g is required.

Blood samples

At least 8 ml of blood in a blood vacuum tube, free from contamination with faeces etc.

Serum samples

At least 2 ml of serum should be submitted.

Blood smears

Thick air dried smears should be prepared, taking care to leave one end of the slide clean. They should be dry before being wrapped in paper.

Suspected toxic material

Suspected material, feedstuffs or plants should NOT be sent unless appropriate specimens from affected animals have also been sent.

At least 50 g of material should be forwarded.

Plant material

Examination for nitrate nitrite and cyanide are best performed in the field.

Plants for identification should be pressed and dried. Refer section Poisoning - plant for submission of plants for identification.

Ingesta

Nitrate and nitrite disappears rapidly from ingesta, and thus ingesta is of no value in diagnosing nitrate/nitrite poisoning.

For other chemical poisons, eg. arsenic, lead, at least 250 g of ingesta should be submitted in an air tight, leakproof container.

Storage and Despatch of Specimens

Tissues should be frozen. Herbage and ingesta samples for toxin examination should also be frozen. Other animal specimens should be chilled.

Interpretation of arsenic, lead and copper concentrations in cattle and sheep

Analyte	Sample	Units	Deficient	Normal	Toxic
Arsenic	Liver	mg/kg (wet wt)		< 0.5	*> 8
Lead	EDTA blood	µg/kg (wet wt)		< 1.2	> 1.2
	Kidney	mg/kg (wet wt)		< 4	> 25
	Faeces	mg/kg (wet wt)		< 10	> 25
Copper	Liver	mg/kg (wet wt)	< 4	**20-70	***> 100
	Kidney	mg/kg (wet wt)	< 4	4-6	> 8

* Liver arsenic may be in range 2 to 8 mg/kg if several days elapsed since toxic exposure.
** Typical liver copper for cattle is > 20 and sheep > 40.
*** In sheep, liver copper may increase up to 200 mg/kg (wet wt) before poisoning occurs

NB.

Interpret concentrations between normal and toxic according to clinical and pathological findings.
Concentrations based on dry wt are approximately 5 times the above (wet wt) values.
Conversion from mg/kg to SI units is as follows:
- As mg/kg x13.3 = As µmol/kg
- Pb mg/kg x 4.8 = Pb µmol/kg
- Cu mg/kg x 0.0157 = Cu mmol/kg