Sampling for Toxicology Screens

These guidelines to collect samples suitable for most toxicological analyses are recommended even if a toxin is not suspected at the time of necropsy.

Please note: there is no complete screen for all known toxins. Test requests should be guided by clinical signs and other diagnostic findings, including clinical pathology, radiology, postmortem examination, and histopathology. A board-certified veterinary toxicologist is available to discuss individual cases, recommend appropriate testing, and guide sample selection once a specific toxin or class of toxins is suspected. Contact the laboratory in advance of sending cases involved in litigation or forensic investigations that require chain of custody handling and, if possible, in advance of sample collection.

Sample Collection: General Guidelines

Always wear appropriate personal protective equipment when collecting potentially hazardous samples and performing necropsy exams. Changing gloves between samples reduces cross-contamination and may be instrumental in assessing differences in toxin concentrations to determine route of exposure and tissue distribution.

  • Ideally, collect samples in unbreakable containers. Zipper storage bags or plastic cups are generally suitable, but may not be best for some toxins. If a specific toxin is suspected, contact the Lab for further guidance.
  • Ensure adequate quantity for toxicology analysis: collect fist-sized pieces of tissue and gallon bags or more of environmental material or feed when possible.
  • Separate material into individual containers and label appropriately (e.g. tissue type, animal ID). Ensure containers are tightly sealed.
  • Begin with least contaminated areas, and end with most contaminated areas.

Depending on the likeliest route of exposure to the suspected toxin(s), environmental or feed sample collection may also aid in diagnosis. A careful walk of the premises may reveal important information such as a break in a fence or presence of foreign material. Questions to consider include:

  • Is feed stored appropriately to prevent spoilage?
  • Is there visible mold or contamination in feedstuffs, or do they smell odd?
  • Are feed, pesticides, or household chemicals stored and labeled properly?
  • Who has access to the animal or premises?
  • What are potential environmental risks? Are there recent changes to the environment, feed or medication source or supplier, or the animals’ management?
  • Do animals have access to trash, outbuildings, building materials, medications, toxic plants, or substances provided by non-caretakers?

Sample Collection: Living Patients

Most frequently, the samples of choice for a live animal are:

  • Heparinized or EDTA whole blood
  • Urine
  • Vomitus or reflux
  • Serum (in royal blue-top trace mineral tube for zinc)
  • Related environmental or feed samples (e.g., paint chips, bait, water, etc.)

If environmental or feed samples are collected, provide any additional pertinent information (e.g. original location found, lot numbers, ingredients list) available to aid in diagnosis, analysis, and follow-up.

Sample Collection: Deceased Patients

This list assumes that the prosector also collects a complete set of formalin-fixed tissues for histopathology, which is relevant in determining appropriate toxicology analyses. Please note that sample sizes required for toxicological analysis are much larger than for histopathology.

The classic necropsy fresh/frozen sample set for suspected toxins includes:

  • Brain
  • Liver
  • Kidney
  • Fat
  • Urine
  • Aqueous humor, or intact eyeball
  • Skin or muscle if site of exposure (e.g., injection site) (Change gloves and clean collection instruments between samples.)
  • Heart blood
  • Stomach or rumen content, and intestinal content or feces (Collect these last. Change gloves and clean collection instruments in between sampling.)

Related environmental or feed samples (e.g. paint chips, bait, water) may also be appropriate. Provide any additional pertinent information (e.g. original location found, lot numbers, ingredients list) to aid in diagnosis, analysis, and follow-up.

Sample Storage and Submission

Ideally, fresh tissue or GI samples should be kept frozen until and during shipping. If cyanide is suspected, freeze samples upon collection. Other sample types usually may be kept cold for storage of less than one week. Do not freeze whole blood. For longer-term storage, consult the Lab.

A complete history is requested, including any drugs administered to the animal. This enables the toxicologist to review the case to ensure the proper analysis is being performed, prevents unnecessary or unwarranted analysis, and lowers costs to the submitter.

In cases where commercially produced feed contamination is suspected, we recommend this be reported to the FDA. Documented complaints assist in assessing food chain risks.

Toxicological Investigation

The goals of the toxicology investigation are to:

  • Identify the source(s) of the toxicant
  • Identify factors contributing to morbidity or mortality
  • Assess the level of contamination
  • Assess possible interventions
  • Assess any risk to the food chain

All cases of evident or suspected toxicosis are reviewed by the toxicologist, and the Lab will contact submitters directly to discuss recommendations for testing, treatment, and next steps.

VSS-WEB-088-V03 09/20/2023