Intracellular and extracellular blood magnesium fractions in hemodialysis patients; is the ionized fraction a measure of magnesium excess?

Abstract

To establish the best measure for determining magnesium overload, we measured ionized and total magnesium in serum and mononuclear blood cells and total magnesium in erythrocytes in blood of 23 hemodialysis patients, known for their disturbed magnesium homeostasis. When comparing the mean magnesium values obtained in the patient population with those of a control population, all of these magnesium markers, including the biologically active fractions, were significantly (P <0.05) increased. Because serum total magnesium was not increased in all dialysis patients studied, the population was divided into two groups, according to total serum magnesium >1.0 mmol/L or less than that. Results in these two populations showed that ionized serum magnesium and ionized magnesium in mononuclear blood cells might give a better indication about the magnesium status of the tested patients than the currently used total serum magnesium data. However, neither of the two markers, especially ionized serum magnesium, was able to discriminate fully between normal magnesium homeostasis and magnesium excess. We therefore conclude that the two ionized magnesium markers offer minimal advantage for this discrimination, and that the total magnesium concentration in serum remains the measurement of choice.

Intracellular free magnesium concentration in healthy horses

“…This is the first study that examines the intracellular magnesium concentration as a diagnostic tool in healthy horses. In human medicine, the need for a more sensitive marker of magnesium deficiency was identified years ago and different methods for the determination of the intracellular magnesium concentration in multiple tissues, and blood cells have been developed (Huijgen et al, 1998;Reinhart, Marx, Haas, & Desbiens, 1987;Schwinger, Antoni, & Guder, 1987). Intracellular electrolyte measurements have been performed in platelets (Niemela, Csako, Bui, & Elin, 1997;Yoshimura et al, 1998), lymphocytes (Delva et al, 2006;Princi et al, 1997) and erythrocytes (Basso, Ubbink, & Delport, 2000).…”

“…The mean free intracellular magnesium concentration measured in this study in healthy horses was slightly lower than the mean values described in healthy humans. Depending on the used method, rather different intracellular magnesium concentrations in healthy humans have been stated, ranging from 0.16 mmol/L (Huijgen et al, 1998) (1998) compared the two fluorescent probes mag-indo 1 and magfura 2. Mag-fura 2 has also been used in this study, which could be one explanation for the comparably low values in our study population.…”

Magnesium basics

“…To date, three major approaches are available for clinical testing ( Table 4 ). The most common test for the evaluation of magnesium levels and magnesium status in patients is serum magnesium concentration [ 21 , 56 ], which is valuable in clinical medicine, especially for rapid assessment of acute changes in magnesium status [ 17 ]. However, serum magnesium concentration does not correlate with tissue pools, with the exception of interstitial fluid and bone.…”

Magnesium in chronic kidney disease Stages 3 and 4 and in dialysis patients

“…Because young erythrocytes have a higher magnesium concentration than older cells [ 31 ], it might be expected that patients on dialysis would have a higher red blood cell magnesium concentration. In fact, the average magnesium concentration of erythrocytes was found to be consistently higher in several studies when patients on dialysis were compared with healthy volunteers [ 32 , 33 , 34 ] or to non-dialysed patients with impaired renal function [ 35 ]. However, patients with higher haematocrit levels (i.e.…”

“…>30%; [ 32 ]) or undergoing erythropoietin treatment [ 34 ] had little difference in their erythrocyte magnesium concentration compared to healthy controls and moreover there was a significant inverse correlation between the magnesium concentration of erythrocytes and haematocrit in patients on chronic dialysis [ 32 ]. In one study, there was a correlation between total and ionized serum magnesium concentrations and total intracellular erythrocyte magnesium concentrations [ 33 ]. In contrast, total magnesium levels in mononuclear cells were not related to serum magnesium levels and were not discriminative for detection of magnesium overload [ 33 ].…”