Texas Equine Veterinary Association

www.texasequineva.com • Page 17 because it provides insight into what might be in the animal's system at the time of collection or within a reasonably short period of time. Urine testing is also beneficial as it can provide information about what a horse might have been exposed to several days or even weeks prior to sample collection. This is achieved by not only screening for the parent drug, but its metabolites as well. In addition to testing urine and serum, we also have the capability to test other matrices that an equine veterinarian may feel are of value. For example, we can screen feed samples for various drugs. We also have the ability to test medications and drug solutions. This request is often made to ensure no other drugs are present in the solution or to verify the concentration listed on the label. Occasionally we receive unlabeled suspected drug solutions for identification and test these as unknowns. Other biological matrices that we can test include whole blood, liver, kidney, stomach contents and ocular fluid. A minimum of 20 grams of tissue, stomach contents or feed are required for testing. Turnaround times for the Equine Pre-Purchase Drug Screen and NSAID Screen are one to three business days. Turnaround times for all other screens and testing services are five to 10 business days. Sample Collection and Submission Sample volume is often times a limiting factor in drug testing. Our testing procedures consist of a screening phase followed by confirmation testing. If a sample is deemed suspect from the initial screening, the sample is re-extracted using a new aliquot from the original container. Drug-specific controls are also extracted and tested alongside the sample. This confirmation test is used to determine whether a sample is reported as positive or negative. Because testing often involves a two-part process, we recommend veterinarians submit a minimum of 10cc of serum or 20cc of urine. This is especially important if a sample tests suspicious during initial screening and requires confirmation testing. Samples should be shipped chilled using an overnight courier. Serum samples with considerable hemolysis can pose problems and impair identification of some drugs. Analytical Testing Analytical testing capabilities for drug testing have evolved significantly over the years. Historically, techniques such as thin layer chromatography (TLC), gas chromatography (GC) and gas chromatography—mass spectrometry (GC/MS) were used to detect drugs. More modern day tests include enzyme- linked immunosorbent assay (ELISA), high-pressure liquid chromatography (HPLC) and liquid chromatography—mass spectrometry (LC/MS). The Drug Testing Lab has experienced staff with state-of-the-art equipment. A variety of NSAIDs can mask lameness, even in a thorough pre-purchase exam. Currently our Drug Testing Lab has transitioned all screening from TLC and ELISA to LC/MS. The advantages to this transition include increased sensitivity, increased sample throughput, more accurate detection and identification, and the ability to screen for hundreds to thousands of drugs in a single analysis. This transition also allows us to evaluate and add new drugs as needed. LC/MS technology also allows us to quantitate drug concentrations in samples. Newer technology has significantly improved sensitivity. We have the capability to test for and quantitate in the picogram per milliliter (parts per trillion) range for some drugs. Routine drug testing is performed on a qualitative (presence or absence) basis. If a sample is confirmed positive, quantitative testing can be performed for an additional fee. Limitations in Drug Testing While advancements in analytical equipment over the years have had many positive attributes, some limiting factors still exist. One such factor is sensitivity. The ability of these machines to detect and quantitate drugs at very low levels has generated questions involving threshold levels used in regulatory testing. With increased instrument sensitivity, equine veterinarians need to consider what questions they are trying to answer when requesting a drug test in a horse. Interpretation of results can vary greatly when comparing "zero tolerance" with a therapeutic or threshold level drug. If a drug is confirmed at a very low level, one must consider whether any physiologic or clinically apparent benefit was present at the time of sample collection. One other limiting factor associated with drug testing relates to the evolution of drugs and drug classes. Proteins, peptides, and some endogenous compounds are becoming more popular. While the technology to detect these substances in biological matrices exists, some require a significant amount of time and resources. Summary Understanding how drug tests are conducted and what tests are available can make it easier when discussing drug testing with horse owners. Improvements in analytical capabilities have allowed us to refine our testing procedures and offer clients more broad-based screening. We encourage our clients to contact the Drug Testing Lab with any questions. Travis Mays, MS, can be contacted at: 979.845.3414. TVMDL is a proud sponsor of the Texas Equine Veterinary Association.

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