Chapter 22
Toxicology Testing

Suspicion of malicious poisoning (usually by a neighbor) is a common reason for owners to request a necropsy. If unexpected death is defined as death occurring in an apparently healthy animal within a period of 12–24 h with no or minimal clinical signs, at least one study suggests that poisoning (accidental or purposeful) is the second leading cause of unexpected death in dogs (Olsen and Allen 2020). In cases where malicious poisoning is suspected, we recommend referring the case for a full gross and histopathologic examination by a board-certified pathologist. If referral is not possible or if the case has no legal implications, this chapter covers the basics of collecting and submitting samples for toxicology testing.

Toxicology testing is relatively simple and reasonably priced if you know what you want to test for. However, tests to identify unknown toxins, such as mass spectrometry and liquid chromatography, tend to be much more expensive. Postmortem toxicology can determine whether a substance, such as a drug, is present in tissue, but often cannot determine how much of the drug was given, since the postmortem breakdown kinetics of most drugs are not known. Also, postmortem redistribution can greatly alter the concentration of a drug in a particular tissue. The best samples for toxicology are refrigerated or frozen (not fixed) pieces of tissue or fluids. These 10 samples are most commonly used for toxicology testing (Figure 22.1):

Liver
Kidney
Spleen
Lung
Fat
Brain
Blood
Urine
Eye
Stomach content

Ten labeled bags from a to j with toxicology samples of liver, lung, kidney, spleen, brain, urine, eye, fat, stomach contents, and blood. — Figure 22.1 Recommended samples for toxicology testing. (a) Liver; (b) Lung; (c) Kidney; (d) Spleen; (e) Brain; (f) Urine; (g) Eye; (h) Fat; (i) Stomach contents; (j) Blood.

If a sample of water, feed, or suspected bait is available, that should also be submitted. Ideally, 5–10 g of tissue, 2–4 ml of blood, or 10–20 ml of other body fluids should be collected. These samples are stored in zipper lock bags or redtop tubes, and chilled or frozen until needed. If ingestion of toxic plants is suspected, examination of the stomach contents may be useful. Indications for common toxicology tests in animals and appropriate samples are listed in Table 22.1.