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- Author or Editor: Stacy H. Tinkler x
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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.
Objective—To determine whether plasma total CO2 concentrations would vary with the size of the evacuated tube used to collect blood samples.
Design—Randomized crossover study.
Animals—Convenience sample of 20 healthy adult horses.
Procedures—Jugular venous blood was collected from horses in random order into 8 types of evacuated tubes: 2-mL glass, 2- or 3-mL plastic or plastic plasma separator, 4- or 6-mL plastic, and 10-mL glass or plastic. Total CO2 concentrations in plasma were measured with a biochemistry analyzer. Data were analyzed via repeated-measures ANOVA and multivariate regression.
Results—The air volume-to-blood volume ratio was significantly higher and consequently, plasma total CO2 concentration was significantly lower when blood was collected into 2-mL glass tubes and 2- or 3-mL plastic tubes than when the other 5 types of evacuated tubes were used. Concentrations in the other tube types were statistically equivalent. A linear relationship was detected between total CO2 concentration and air volume–to–blood volume ratio.
Conclusions and Clinical Relevance—Blood samples should be collected into evacuated tubes with a small air volume–to–blood volume ratio whenever an accurate estimate of plasma total CO2 concentration is required.