Evaluation of an ionized magnesium-pH analyzer-NOVA 8

Abstract

An ion - selective analyzer (NOVA 8 [previously NOVA CRT], NOVA Biomedical, Waltham, USA) for simultaneous measurement of the concentration of ionized magnesium (cMg²⁺) and pH is investigated for linearity and influence of calcium ions on the Mg²⁺ results in different Mg²⁺ aqueous solutions with/without added calcium. Within the cMg²⁺ range 0-3.0 mmol/L, which covers most clinical values, we found cMg²⁺ values close to the line of identity, with a sensitivity about 94%, but 0.09 mmol/L lower in the absence of Ca²⁺. The analytical precision (CV) for human serum control was 1.7% in the physiological range. The accuracy and precision data for the Mg²⁺ electrode meet the demands for reliable results within the range for clinical use. We found a reference interval (95%) for cMg²⁺ of between 0.43 and 0.59 mmol/L in serum, with a mean value of 0.51 mmol/L for healthy adults in the non - fasting state with no relation to sex or age. The mean cMg²⁺ was 61% of the mean concentration of plasma total magnesium (cTMg) ranging from (95%) 49% to 73%. No significant correlation was found between cMg²⁺ and total protein, albumin, phosphate, Ca²⁺, and total CO₂. No significant difference was found between mean values for cMg²⁺ in whole blood, plasma, and serum. Serum samples could be stored for 24 h at 4%C without significant change. Storage at -20°C for 7 months caused a mean cMg²⁺