Evaluation of an electrolyte analyzer for measurement of ionized calcium and magnesium concentrations in blood, plasma, and serum of dogs.

Objective: To evaluate an electrolyte analyzer for measurement of ionized calcium (Ca(i)) and magnesium (Mg(i)) concentrations in blood, plasma, and serum; investigate the effect of various factors on measured values; and establish reference ranges for Ca(i) and Mg(i) in dogs.
Animals: 30 healthy adult dogs of various breeds.
Procedure: Precision in a measurement series, day-to-day precision, and linearity were used to evaluate the analyzer. The effects of exposure of serum samples to air, type of specimen (blood, plasma, or serum), and storage temperature on sample stability were assessed. Reference ranges were established with anaerobically handled serum.
Results: The coefficient of variation for precision in a measurement series was < or = 1.5% for both electrolytes at various concentrations. The Ca(i) and Mg(i) concentrations were significantly lower in aerobically handled serum samples, compared with anaerobically handled samples. The Ca(i) and Mg(i) concentrations differed significantly among blood, plasma, and serum samples. In anaerobically handled serum, Ca(i) was stable for 24 hours at 22 degrees C, 48 hours at 4 degrees C, and 11 weeks at -20 degrees C; Mg(i) was stable for 8 hours at 22 degrees C, < 24 hours at 4 degrees C, and < 1 week at -20 degrees C. In anaerobically handled serum, reference ranges were 1.20 to 1.35 mmol/L for Ca(i) and 0.42 to 0.58 mmol/L for Mg(i).
Conclusions and Clinical Relevance: The electrolyte analyzer was suitable for determination of Ca(i) and Mg(i) concentrations in dogs. Accurate results were obtained in anaerobically handled serum samples analyzed within 8 hours and kept at 22 degrees C.