Table 4.

Magnesium assessment [7, 21]

Magnesium in:

Serum

Red blood cellsa

Leucocytesb

Musclec

Metabolic assessment via:

Balance studies

Isotopic analyses

Renal excretion of magnesium

Retention of magnesium, following acute administration

Free magnesium levels with:

Fluorescent probesd

Ion-selective electrodese

Nuclear magnetic resonance spectroscopyf g

Metallochrome dyes

^aRed blood cell magnesium concentration does not seem to correlate well with total body magnesium status [53].

^bMagnesium content of mononuclear cells may be a better predictor of skeletal and cardiac muscle magnesium content [54].

^cMuscle is an appropriate tissue for the assessment of magnesium status [55] but it is an invasive and expensive procedure requiring special expertise.

^dIntracellular free magnesium concentration can be determined by using fluorescent probes [10]. Application of fluorescent dyes, however, is limited because the major fluorescent dye for magnesium (mag-fura 2) has a higher affinity for calcium than for magnesium.

^eIon-specific microelectrodes can be used to measure the internal free ion concentration of cells and organelles. Major advantages are that readings can be made over long time spans. In contrast to dyes, very little extra ion buffering capacity has to be added to the cells, and direct measurement of the ion flux across the membrane of a cell is possible with every ion passing across the membrane contributing to the result. Nonetheless, ion-selective electrodes for magnesium are not entirely selective for ionized magnesium. A correction is applied based on the ionized calcium concentration [10].

^fTotal magnesium content of a biological sample can be determined by using flame atomic absorption spectroscopy (AAS). However, this technique is destructive and, for optimal accuracy, sample volume has to add up to ∼2 mL with a concentration ranging from 0.1 to 0.4 μmol/L. With this technique, only content, not uptake, can be quantified.

^gNuclear magnetic resonance may be used to measure intracellular free magnesium concentration [10].