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

Abstract

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.

Electrolyte Evaluation

“…1,2 When serially evaluating a patient's electrolytes, values should always be measured with the same methodology and, ideally, the same analyzer because reference ranges and read ings vary between the different methodologies and analyzers. [3][4][5] Flame photometry is typically only avail able in reference laboratories, making it impractical to use this methodology for POC analysis. FF was the gold standard for electrolyte analysis but has become obsolete due to both the logistics of utilization and inaccuracies in measurement with concurrent lipemia, hyperprotein emia, hemolysis, or hyperbilirubinemia.…”

“…Overall, however, electrolyte analysis should be performed on serum samples that are col lected anaerobically. 3,4,[8][9][10][11] Anaerobic conditions are most important for ionized calcium and magnesium analysis. 4,10-12 Whole blood, anticoagulated whole blood, and plasma can also be used, but one must consider various possible artifacts and the risk of clot formation prior to the completion of analysis when using whole blood.…”

“…Careful attention to the timing of the sample collection and measurement is pivotal because various electrolyte concentrations can be affected by increased exposure time to platelets, exposure time to white blood cells, and alterations in protein binding associated with ongoing cellular metabolism (Vetscan iSTAT 1,user guide). 3,4,12 Individual electrolytes Table 49.2 details normal ranges and critical alert values for each of the physiologically significant electrolytes. It is important to remember, however, that these ranges should be used only as guidelines because each analyzer has its own manufacturerdetermined reference inter vals.…”

“…11,37 Total calcium measurements correlate poorly with ionized calcium in situations of renal insufficiency and acidbase imbal ance. 4,12 Total calcium measurement can also be spuri ously affected by hemolysis, hyperbilirubinemia, and lipemia. 11 Ionized calcium assessed by ISE, which mini mizes interference by other ions, protein, hemolysis, and Clinical signs of hyperphosphatemia include weak ness, tetany, seizures, tachycardia, and torsades de pointes, a potentially fatal cardiac dysrhythmia.…”

“…3 Various studies have demonstrated slightly dif ferent results regarding the length of time an ionized calcium sample is stable at varying temperatures, but conservative collective interpretation of these studies indicates that if a sample is not analyzed within 8 hours of collection it should be refrigerated (4°C) for up to 48 hours or frozen at −20°C for up to 1 week. 3,4,12 Sodium and lithium heparin bind or chelate calcium, which causes ionized calcium to drop. 3,8,11 Zinc heparin displaces calcium from binding sites and causes ionized concentrations to increase.…”