Total Carbon Dioxide in Adult Standardbred and Thoroughbred Horses.
Authors: Lindinger Michael Ivan
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Total Carbon Dioxide in Adult Standardbred and Thoroughbred Horses Racing authorities have long relied on blood total carbon dioxide (TCO2) testing to detect performance-enhancing alkalising agents, but Lindinger's comprehensive review reveals this approach is far more complex than previously recognised. Through systematic analysis of published research on Standardbred and Thoroughbred populations, the author identified that TCO2 concentration is influenced primarily by changes in strong ion concentrations and weak acids (particularly plasma albumin), rather than alkalising agent administration alone. The natural range of TCO2 in non-treated racehorses spans 23–38 mmol/L—considerably wider than regulatory frameworks typically acknowledge—with physiologically normal elevations occurring independently of any doping practice in response to feeding, circadian rhythms, seasonal factors and exercise patterns. Crucially, hour-by-hour variation data remain sparse, and existing population studies lack robust validation methods to confirm whether horses were actually treated with alkalising agents, undermining confidence in historical findings. For practitioners and regulators alike, this work underscores that a single TCO2 measurement cannot reliably diagnose alkalising agent use and highlights the urgent need for longitudinal individual baselines, improved testing protocols, and greater appreciation of the substantial biological variation that characterises acid–base status in racing horses.
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Practical Takeaways
- •Wide normal TCO2 range means single TCO2 tests have limited diagnostic value for detecting performance-enhancing alkalizing agents in racehorses
- •Understand that natural variations from diet, time of day, and training cause significant TCO2 fluctuations—serial measurements and contextual information are needed for meaningful interpretation
- •Regulatory testing programs should account for individual baseline variation and temporal patterns rather than relying on absolute TCO2 values alone
Key Findings
- •Normal TCO2 in non-alkalized Standardbred and Thoroughbred horses ranges from 23-38 mmol/L, significantly wider than previously appreciated
- •TCO2 is primarily affected by strong ion concentration changes, followed by weak acid (plasma albumin) concentration changes
- •Independent of alkalizing agents, TCO2 varies with feeding, diurnal rhythm, season, and exercise
- •TCO2 testing alone is not definitive for detecting alkalizing agent administration in racehorses