Objective-To determine the degree of agreement between 2 analyzers for measurement of total CO2 concentration (ctCO2) in equine plasma. Animals-6 healthy untrained horses, 6 trained Standardbreds undergoing a simulated race protocol, and 135 trained Standardbreds at a racetrack. Procedures-Jugular venous blood samples were obtained from all horses. Two analyzers (commonly used analyzer A and less expensive analyzer B) were used to measure plasma ctCO2 in each sample. Validation of both analyzers was conducted in accordance with guidelines established by the Clinical and Laboratory Standards Institute and involved characterization of linearity, total analytic error, and bias estimation. Results-Total analytic error (instrument SD) was 0.58 mmol/L (coefficient of variation, 1.6%) and 0.49 mmol/L (coefficient of variation, 1.4%) for analyzers A and B, respectively, when measuring an aqueous standard containing 36.0 mmol of CO2/L. A 1 g/L decrease in plasma protein concentration corresponded to an increase in ctCO2 measured with analyzer B of 0.065 mmol/L. A difference plot indicated that analyzer B produced values 2.7% higher than analyzer A for 103 samples from the 6 trained and exercised Standardbreds (mean plasma protein concentration, 67 g/L). Conclusions and Clinical Relevance-Analyzer B provided adequate precision and linearity for measurement of ctCO2 from 5 to 40 mmol/L and was therefore suitable for measuring ctCO2 in equine plasma, provided allowances are made for changes in plasma protein concentration.
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