Equine total carbon dioxide testing in Illinois in 2012

During prolonged strenuous exercise, racehorses can experience acidemia. To counteract this phenomenon, trainers can administer blood alkalizing agents that raise the plasma pH and total carbon dioxide (TCO₂) concentration. In Illinois, the administrative threshold for TCO₂ in plasma is 37.0 mmol/L. Because accuracy in the reported measurement of TCO₂ must be ensured, uncertainty measurements are often issued alongside the reported concentrations. We report a validated method for measuring TCO₂ levels in equine plasma using the Beckman UniCel DxC 600. A six-point calibration curve ranging from 5 to 50 mmol/L is analyzed along with controls at four TCO₂ levels with each set of samples. Using this method, we collected data from 5,199 race samples during 2012, with 134 being from thoroughbred horses and 5,065 from standardbred horses. During method validation, uncertainty was determined using the simplified Guide to the Expression of Uncertainty in Measurement approach and was found to be 3% at 99.7% confidence level with eight measurements. Additionally, to investigate other variables that could have an effect on TCO₂ levels, we collected the gender, breed, Lasix® status, strong ion concentration, pre-or post-race collection time and track location of all horses tested during that year. The samples had an overall mean TCO₂ concentration of 30.5 ± 2.0 mmol/L. The other physiological and environmental datawere analyzed using analysis of covariance tables. These results indicate gender, breed, furosemide status, collection time and track location to be strongly correlated (P < 0.0001) to TCO₂ levels. Thoroughbred status was found to have no effect. Finally, TCO₂ concentrations were highly correlated (P < 0.0001) to sodium and chloride ion concentrations. No correlation was found between TCO₂ and potassium concentrations. The results show that there are several environmental and physiological factors that can affect TCO₂ concentrations. The concentration of other strong ions present in the blood may indicate doping status.