Veterinarians screen racehorses regularly for evidence of performance enhancers, aiming to use sample collection methods that yield accurate and consistent results. Blood-draw supplies vary among veterinarians, however, and could conceivably impact test results, so a Purdue University research team recently evaluated how such variables impact a common measurement used in drug testing–total plasma carbon dioxide (CO2) concentrations.

Stacy Tinkler, DVM, Dipl. ACVIM, clinical assistant professor of equine community practice at the Purdue University College of Veterinary Medicine, and colleagues compared blood tube size and material, and she presented their results at the 2012 American Association of Equine Practitioners convention, held Dec. 1-5 in Anaheim, Calif.

Regulators test total CO2 concentrations in racehorses’ blood to determine if trainers or caretakers administered alkalinizing substances, also known as "milkshakes." These mixtures of bicarbonate and/or other alkaline substances, considered moderate performance enhancers in human athletic arenas, are administered to horses shortly before they compete. Some believe the mixtures delay lactic acid buildup in muscles, allowing horses to run farther before tiring, although "the jury is still out on whether or not … administration actually has a beneficial effect on performance in the horse," Tinkler said. Regulators test for excess blood carbon dioxide before or after a race, depending on the particular track’s testing protocol.

Veterinarians know that under-filling tubes when collecting blood for total CO2 concentration measurement can yield lower values. And Tinkler noted that even when tubes are filled completely and according to manufacturer’s instructions, they can yield different air-to-blood ratios, depending on their size and expected draw volume