Fractionation of canine serum magnesium

Abstract

Serum total magnesium (tMg) consists of 3 fractions: ionized magnesium (iMg), protein-bound magnesium (pbMg), and complexed magnesium (cMg). Serum iMg may be measured by an ion-selective electrode, but determination of pbMg and cMg has not been attempted in dogs. The objectives of this study were to assess the validity of a micropartition system to fractionate serum tMg and to establish reference intervals for pbMg, cMg, and iMg in clinically normal dogs using this method. Serum samples from 10 clinically healthy dogs were fractionated using a micropartition system (Centrifree YM-30, Amicon Corp, Lexington, MA, USA). Serum tMg and iMg were measured in whole serum, and tMg was also measured in the ultrafiltrate. Concentration of cMg was obtained by the subtraction of iMg from tMg concentrations of the ultrafiltrate. Protein-bound Mg was calculated by subtracting the tMg concentration of the ultrafiltrate from the tMg concentration of whole serum. Results for pbMg and cMg using the micropartition system showed good reproducibility. Determination of tMg and iMg had acceptable inter- and intra-assay precision. Concentrations of iMg, cMg, and pbMg were 0.50 +/- 0.05 mmol/L, 0.05 +/- 0.04 mmol/L, and 0.24 +/- 0.04 mmol/L, representing 63%, 6%, and 31% of the tMg concentration, respectively. The micropartition system was a reproducible means to accurately assess cMg and pbMg concentrations in dogs.