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 data were 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.