Comparative findings on serum IMg2+ of normal and diseased human subjects with the NOVA and KONE ISE's for Mg2+

Systematic Review and Meta-Analysis to Estimate a Reference Range for Circulating Ionized Magnesium Concentrations in Adult Populations

BACKGROUND

There is a lack of consensus on a reference range for ionized magnesium (iMg2+) in blood as a measure of the status of circulating iMg2+ for the screening of populations.

OBJECTIVES

We estimated the reference range of iMg2+ levels for healthy adult populations and the ranges for populations with cardiovascular disease (CVD), type 2 diabetes, hypertension, and renal disease. We also estimated 95% ranges for circulating magnesium (Mg) in healthy and those with cardiometabolic diseases.

METHODS

We searched Ovid MEDLINE, Cochrane Central Register of Controlled Trials, and Embase through 24 July, 2020 to identify articles. We included English, peer-reviewed, randomized controlled trials, prospective and retrospective cohort studies, case-control studies, and cross-sectional studies that measured iMg2+ in blood or circulating Mg at baseline. The protocol was registered on PROSPERO (CRD42020216100). Estimated ranges were calculated by employing a frequentist random-effects model using extracted (or calculated) means and SDs from each included study. We determined the 95% confidence interval of the pooled mean.

RESULTS

A total of 95 articles were included with 53 studies having data for healthy participants and 42 studies having data for participants with cardiometabolic diseases. The estimated reference range for iMg2+ for healthy populations was 0.40-0.68 mmol/L, 0.38-0.64 mmol/L for CVD, 0.34-0.66 mmol/L for type 2 diabetes, 0.39-1.04 mmol/L for hypertension, and 0.40-0.76 mmol/L for renal disease. For circulating Mg, the estimated range was 0.72-1.0 mmol/L for healthy adults, 0.56-1.05 mmol/L for CVD, 0.58-1.14 mmol/L for type 2 diabetes, 0.60-1.08 mmol/L for hypertension, and 0.59-1.26 mmol/L for renal disease.

CONCLUSIONS

Estimated reference ranges for cardiometabolic disease states for both iMg2+ and circulating Mg were broad and overlapped with the estimated range for healthy populations (0.40-0.68 mmol/L). Further studies should evaluate whether iMg2+ can be used as a biomarker of cardiometabolic disease.

Serum ionized magnesium and calcium levels in adult patients with seizures

OBJECTIVE

Prior studies have been equivocal about whether or not serum levels of the divalent ions calcium and magnesium are altered during different types of seizures. Magnesium is a potential modulator of seizure activity because of its ability to antagonize the excitatory calcium influx through the N-methyl-D-aspartate (NMDA) receptor. We hypothesize that serum ionized levels of calcium (Ca(2+)) and magnesium (Mg(2+)) would be altered significantly during certain types of seizures.

MATERIAL AND METHODS

A convenience sample of seizure patients presenting to an emergency department (ED) were enrolled in this prospective study. Novel ion-selective electrodes were used to measure Ca(2+) and Mg(2+). Data were reported as mean values+/-standard deviations. Group comparisons were analyzed by ANOVA with post-hoc testing using the Bonferroni, or the Fisher exact test, where appropriate, alpha = 0.05 (two-tailed).

RESULTS

Forty-nine patients with seizure and 32 healthy racially matched controls were included in the study. Seizure patients had a significantly (p<0.001) lower mean Mg(2+), but not total serum Mg and a significantly (p<0.001) higher Ca(2+)/Mg(2+) ratio than that in controls.

CONCLUSIONS

We were able to show significantly lower Mg(2+) and higher ionized Ca(2+)/Mg(2+) ratios in seizure patients compared with a racially matched control group.

Ionized magnesium in erythrocytes—the best magnesium parameter to observe hypo- or hypermagnesemia

BACKGROUND

Almost 99% of the body magnesium is inside cells. The concentration of intracellular ionized magnesium (iMg) is physiologically relevant. iMg in erythrocytes is a new parameter that can help to establish reliable information on the functional magnesium status.

METHODS

iMg concentration in erythrocytes and serum was measured by ion-selective electrode, in clinical analyzer Microlyte (KONE). Total magnesium (tMg) concentration was measured by atomic absorption spectrometry (AAS). Albumin and total protein concentration were measured colorimetrically.

RESULTS

In critically ill postoperative patients, the mean of albumin, protein and hematocrit concentration was significantly lower compared to healthy individuals. Hypomagnesemia was found in 15.9% patients as tMgs, at 22.2% as iMgs and 36.5% as iMge. Significant correlations are between iMgs and tMgs or iMge and iMgs/tMgs. In dialyzed patients, the mean of hematocrit was significantly lower, iMge was significantly higher compared with healthy individuals. Significant negative correlations are between iMgs and tMge or iMge/tMge and tMge.

CONCLUSIONS

iMge is the best magnesium parameter to observe hypo- or hypermagnesemia for both groups of patients. The function of magnesium is mainly intracellular and intracellular magnesium concentrations can be the method to evaluate the magnesium status.

Serum ionized magnesium levels and ionized calcium-to-magnesium ratios in adult patients with sickle cell anemia

Low levels of total magnesium in sickle cell erythrocytes have been linked to increased sickling due to cell dehydration. We tested the null hypothesis that adult sickle cell anemia (SCA) patients have the same serum level of ionized Mg (Mg(2+)) and Ca(2+)/Mg(2+) ratio as healthy African Americans (AA) and healthy Caucasians (CAUC). We measured serum Mg(2+) and ionized calcium (Ca(2+)) with ion-selective electrodes and calculated the serum Ca(2+)/Mg(2+) ratios in patients with SCA and control groups (AA and CAUC). Seventy-four SCA patients and 61 controls were compared. SCA patients had significantly (P < 0.001) lower levels of serum Mg(2+) (0.52 +/- 0.05) compared to healthy AA (0.57 +/- 0.04) and CAUC (0.62 +/- 0.03). Eighty-six percent of the adult SCA patients had serum Mg(2+) levels below the mean for the AA group, and 96% of SCA patients were above the AA group's mean serum Ca(2+)/Mg(2+). Of the SCA patients studied, 25.6% (95% CI, 16.2-37.2%) had serum Mg(2+) levels below the racially adjusted lower limit of normal and 50% (95% CI, 38.1-61.9%) were above the upper limit of serum Ca(2+)/Mg(2+) for AA controls. By measuring serum Mg(2+) and Ca(2+), we were able to define a subset of SCA patients with hypomagnesemia and elevated Ca(2+)/Mg(2+) ratios, who may benefit from magnesium supplementation.

Evaluation of two Mg2+-selective electrodes by means of a flow-through device

Monitoring the ionized magnesium (Mg2+) concentration in critically ill patients can prevent development of serious and potentially fatal complications. The analyzers KONE Microlyte 6 (KONE Instruments, Espoo, Finland) and NOVA CRT (NOVA Biomedical, Waltham, MA, USA) provide the discontinuous measurement of Mg2+ and were evaluated in several studies. It was our objective to integrate the Mg2+-selective electrodes into a device for continuous on-line measurements. This device is suitable not only for research but also for a specific evaluation of electrode characteristics. It allowed us to compare the genuine electrodes and reference systems independently of their specific analyzers. Precision, accuracy, response time, limit of detection, drift and interferences were assessed by continuous flow-through measurements and discussed in comparison to the results of previous studies. The NOVA electrode proved to be superior regarding accuracy, sensitivity and selectivity, especially with respect to calcium. It was demonstrated that current commercial serum-like control materials were not appropriate for quality control of the assessed Mg2+-electrodes. However, despite the fact that the electrodes are commercially used for discontinuous measurements, both sensor types can be used for continuous on-line measurements in an extracorporeal circulation in a rat model. The NOVA electrode showed superior characteristics with this application as well. This study should also be understood as a contribution to the development of devices for online analyzers used in point-of-care-testing.

Magnesium. An update on physiological, clinical and analytical aspects

There is an increased interest in the role of magnesium ions in clinical medicine, nutrition and physiology. The characteristics of the binding of magnesium and calcium ions to various components, macromolecules and biological membranes are described. Magnesium affects many cellular functions, including transport of potassium and calcium ions, and modulates signal transduction, energy metabolism and cell proliferation. The mechanism of cellular uptake and efflux of magnesium, its intracellular transport, intestinal absorption, renal excretion and the effect of hormones on these are reviewed. Magnesium deficiency is not uncommon among the general population: its intake has decreased over the years especially in the western world. The magnesium supplementation or intravenous infusion may be beneficial in various diseased states. Of special interest is the magnesium status in alcoholism, eclampsia, hypertension, atherosclerosis, cardiac diseases, diabetes, and asthma. The development of instrumentation for the assay of ionized magnesium is reviewed, as are the analytical procedures for total magnesium in blood and free magnesium in the cytosol. The improved procedures for the assay of different magnesium states are useful in understanding the role of magnesium in health and disease.

Serum ionized magnesium and calcium and sex hormones in healthy young men: importance of serum progesterone level

OBJECTIVE

To determine the serum concentrations of the sex hormones with respect to the concentrations of the biologically active fractions of magnesium (Mg) and calcium (Ca) in healthy young men and to compare them with those in young and older women.

DESIGN

Controlled clinical study.

SETTING

An academic research environment.

PATIENT(S)

Twenty-five healthy young male volunteers.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Concentrations of the sex steroid hormones testosterone, estrogen, and progesterone, and levels of ionized Ca (Ca2+) and Mg (Mg2+) were measured in the serum of healthy young men. These levels were compared with those in young women at different phases of the menstrual cycle and with those in older women.

RESULT(S)

The Mg2+ and total Mg concentrations in young men were not different from those during the follicular phase in young women or from the mean concentrations in menopausal women. The Ca2+ levels in young men were similar to the levels in young women during the follicular phase but significantly lower than the levels in older women. The Mg2+ concentration in the young men was directly and significantly related to the progesterone level, and the Ca2+/Mg2+ ratio was inversely related to the progesterone level.

CONCLUSION(S)

Progesterone may be a more important steroid hormone in men than previously believed.

Extracellular magnesium regulates effects of vitamin B6, B12 and folate on homocysteinemia-induced depletion of intracellular free magnesium ions in canine cerebral vascular smooth muscle cells: possible relationship to [Ca2+]i, atherogenesis and stroke

Homocysteine (HC) at concentrations of from 0.05 to 1.0 mM caused dose-dependent loss of [Mg2+]i in cultured cerebral vascular smooth muscle cells (VSMC), whereas cysteine and methionine (its metabolic products) failed to interfere with changes in [Mg2+]i. HC, methionine and cysteine did not produce any changes in [Ca2+]i. Lowering [Mg2+]o to 0.3 mM resulted in elevation of [Ca2+]i and loss of [Mg2+]i. Depletion of [Mg2+]i, induced by HC, was potentiated by low Mg2+. Preincubation of these cells with vitamin B6, vitamin B12, folic acid, alone, did not alter [Ca2+]i or [Mg2+]i. Likewise, concomitant addition of vitamin B6, vitamin B12, or folic acid, together with HC (1 mM) did not change the reduction in [Mg2+]i induced by HC. However, concomitant addition of HC and the three vitamins inhibited completely the loss of [Mg2+]i. Exposure of these cells to each vitamin, alone, or combination of the three vitamins failed to interfere with reduction in [Mg2+]i induced by low [Mg2+]i, but it did suppress the rise in [Ca2+]i. Interestingly, in the presence of low [Mg2+]o, the vitamin combination did not retard depletion of [Mg2+]i. The present findings are compatible with the hypothesis that an increased serum HC concentration causes abnormal metabolism of Mg2+ in cerebral VSMC, thus priming these cells for HC-induced atherogenesis, cerebral vasospasm and stroke. Our results suggest the need for the three B-vitamins, together with normal physiological levels of Mg2+, in order to prevent [Mg2+]i depletion and occlusive cerebral vascular diseases induced by homocysteinemia.

Magnesium modulates contractile responses of rat aorta to thiocyanate: A possible relationship to smoking-induced atherosclerosis

Thiocyanate anions (SCN-) as the end products of tobacco smoke and found in the blood of cigarette smokers have been implicated in atherogenesis and heart diseases. Magnesium deficiency has also been implicated in the etiology of atherogenesis. The contractile responses of rat aorta to SCN- and the modulation of extracellular magnesium ions ([Mg2+]o) on the effect of SCN- were, therefore, studied in isolated rat aortic rings. SCN- exposure at a range of concentrations (from 10(-5) to 5 x 10(-2) M) induces contractile responses of isolated rat aortic rings with and without endothelium in a concentration-dependent manner. Significant differences in responsiveness to SCN- were found in rat aortic ring segments with and without endothelial cells. Preincubation of these vessels with low [Mg2+]o markedly shifted the contractile concentration-effect curves to the left, and the contractile effects of SCN- in rat aortic rings were potentiated. In contrast to lowering [Mg2+]o, increasing [Mg2+]o to 2.4 mM was found to dramatically attenuate the contractile responses to SCN-. In the absence of extracellular Ca2+ ([Ca2+]o), SCN--induced contractions were, however, almost abolished after exposure to Mg2+-free medium. In order to investigate the mechanisms of [Mg2+]o modulation of SCN--induced contractile response of rat aorta, changes in intracellular Ca2+ ([Ca2+]i) were measured in cultured primary smooth muscle cells isolated from rat aorta. The resting level of [Ca2+]i in the rat aortic smooth muscle cells was 80.6 +/- 6.6 nM. Exposure of these cells to SCN- (5 x 10(-5) to 5 x 10(-3) M) produced rises in [Ca2+]i in a concentration-dependent manner. Preincubation of these cells with low [Mg2+]o (0 or 0.3 mM, the lowest physiological range) for 24 h significantly potentiated increments in [Ca2+]i induced by SCN-. These rises in [Ca2+]i induced by SCN- were completely inhibited by pretreating the cells with 2.4 mM [Mg2+]o for 24 h. These results support a hypothesis whereby cigarette smoking or exposure to smoking can induce cardiovascular diseases, at least partly, probably by causing spasm and thickening of arterial blood vessels as a consequence of large rises in [Ca2+]i in vascular smooth muscle cells. The chronic presence of or exposure to both thiocyanate and low Mg2+ in the blood of smokers can result in rapid flux of Ca2+ into vascular smooth muscle cells, thus accelerating or initiating atherosclerotic processes in smokers.

Serum ionized magnesium: comparison of results obtained with three ion-selective analyzers

In a two-center (Academic Medical Center, The Netherlands, and National Institutes of Health, USA) study, we compared ionized magnesium (iMg2+) results in serum determined with the AVL 988/4, KONE Microlyte 6 and NOVA CRT, which are the currently available analyzers equipped with a magnesium ion-selective electrode. The comparison was performed with frozen serum samples from normal individuals and patients. Imprecision and reference intervals were established. We found the best agreement between the KONE(x) and AVL(y) magnesium ion-selective electrodes (y= 0.972x-0.013; n=138) with samples from patients. With samples from normals, all three analyzers reported significantly different results (p<0.05). Best precision was found using the NOVA; coefficients of variation established at three levels were all < 4.0%. Coefficients of variation for the AVL and KONE were <5% at normal and high iMg2+, but 10.7 and 9.4%, respectively, at iMg2+ approximately 0.30 mmol/l. The reference intervals (mean+/-standard deviation) based on measurements in fresh serum samples were different for each analyzer: 0.55-0.63 mmol/l for AVL, 0.470.57 mmol/l for KONE and 0.43-0.55 mmol/l for NOVA. Thus, significant differences among the ionized magnesium concentration obtained with the three analyzers, limit comparison of results in clinical practice, and need to be resolved (e.g. by improvement of specificity and standardization of calibrators).

Mg2+ modulates membrane sphingolipid and lipid second messenger levels in vascular smooth muscle cells

In vitro studies with smooth muscle cells from rat aorta and dog cerebral blood vessels indicate that variation in free Mg2+, within the pathophysiological range of Mg2+ concentrations, found in human serum, causes sustained changes in membrane phospholipids and lipid second messengers. Incorporation of [3H]palmitic acid into phosphatidylcholine (PC) and sphingomyelin (SM) was altered within 15-30 min after modifying the extracellular Mg2+ ion level ([Mg2+]o). Decreased Mg2+ produced a fall in both [3H]SM and [3H]PC over the first 2 h. After an 18-h incubation, the [3H]PC/[3H]SM ratio changed from about 20:1 to about 50:1. Increased [Mg2+]o resulted in a 2- to 3-fold increase in [3H]SM compared to only a small increase in [3H]PC over the same period. There was a reciprocal relationship between [3H]ceramide and [3H]1,2-DAG levels with highest [3H]ceramide and lowest [3H]-1,2-DAG levels seen at lowest [Mg2+]o. The results indicate that a fall in extracellular ionized Mg2+ concentration produces a rapid and sustained decrease in membrane sphingomyelin and a moderate rise in intracellular ceramide. A major effect of lowering [Mg2+]o appears to be a down-regulation of SM synthase. The increased membrane SM content and a concomitant decrease in cell ceramide, in the presence of elevated [Mg2+]o, may be relevant to the apparent protective role of adequate Mg intake on vascular function in humans.

Serum ionized versus total magnesium in patients with intestinal or liver disease

In serum, magnesium exists in three fractions: protein-bound, complex-bound and free ionized form. Only the free ionized fraction is biologically active. Until recently, only the measurement of serum total magnesium has been in clinical use. Now, commercially available instruments using new ion-selective electrodes for Mg++ have made possible the reliable measurement of serum ionized magnesium in clinical practice. For the measurement of serum ionized magnesium we used a magnesium-selective electrode installed in a six-channel electrolyte analyzer. We compared the use of ionized versus total magnesium measurement in 52 patients with intestinal disease, 54 with liver disease, and in 75 healthy control subjects. In the patients with alcoholic liver disease both serum ionized and total magnesium were lower, and in those with inflammatory bowel disease slightly higher than in control subjects. The correlation coefficient between serum ionized and total magnesium was r=0.87 (p<0.001) in the patients, and r=0.75 (p<0.001) in the controls. In the patient group the fraction of ionized magnesium in the total was negatively related to the serum albumin level (r=-0.41, p<0.001). Serum total magnesium was below the reference range in 30 out of 150 measurements, serum ionized magnesium in only 9 out of 150 measurements, respectively. Thus, 21 cases with low total but normal ionized magnesium (two thirds of hypomagnesemia according to serum total magnesium) were false positive. Total magnesium measurement may overestimate the incidence of hypomagnesemia when significant hypoalbuminemia is present. Measurement of serum ionized magnesium instead of total magnesium may therefore be of advantage in evaluating patients with hypoalbuminemia and when hypomagnesemia is expected.

Serum ionized magnesium in premature and term infants

Magnesium is the element with the second highest concentration in the body and is found almost entirely in the intracellular compartment. The small serum component gives a poor representation of the active, physiologic state of the metal. This state is assessed much better by measuring ionized magnesium in the serum, which can now be performed with a sensitive ion-selective electrode. This study was undertaken to establish the normal serum ionized magnesium levels in newborn infants and to define normal serum ionized calcium/ionized magnesium ratios. Ninety-seven infants were investigated. Six were born before 32 weeks gestation, 28 between 33 and 37 weeks gestation, and 63 were term. Ionized magnesium levels were 0.69 +/- 0.14 mmol/L, 0.63 +/- 0.10 mmol/L, and 0.57 +/- 0.07 mmol/L in each group, respectively. These findings demonstrate a significant decline in serum ionized magnesium with increasing maturity. This decrease may relate to a greater need for magnesium uptake during earlier gestation, more magnesium-induced vasodilation to maintain adequate blood flow to developing tissues and organs, or immature parathormone function earlier in pregnancy. The progressive rise in serum ionized calcium/ionized magnesium ratios found herein supports the latter hypothesis.

Ionized magnesium level in whole blood of healthy Japanese children

Magnesium (Mg) catalyzes or activates more than 300 enzymes in the body, and it plays a pivotal role in the metabolism of carbohydrates, fats and proteins. Until recently Mg has only been measured as a total substance concentration; however, it is the free ionized form of magnesium (iMg2+) that is physiologically active. In 1992, a novel ion selective electrode (ISE) utilizing a neutral carrier-based membrane for assessment of iMg2+ in whole blood, plasma or serum was designed and it was used to measure the iMg2+ level in whole blood of 160 healthy Japanese children. There was a significant positive correlation between serum total magnesium (SMg) and iMg2+. Percent ionized magnesium (iMg2+/SMg) was 58.3 +/- 4.1% and increased with growth (age and bodyweight). The level of iMg2+ was 1.29 +/- 0.08 mg/dL (range, 1.09-1.51) ¿0.535 +/- 0.033 mmol/L (range, 0.452-0.627)¿ and was constant irrespective of growth. On the other hand, SMg, serum total calcium (SCa) and ionized calcium (iCa2+) decreased with growth. Thus only iMg2+ level was constant irrespective of growth. It is suspected that the buffer action of protein binding Mg may keep the iMg2+ level constant, because iMg2+ plays an important part in the activation of many enzymes.

Exposure of piglet coronary arterial muscle cells to low concentrations of Mg2+ found in blood of ischemic heart disease patients result in rapid elevation of cytosolic Ca2+: relevance to sudden infant death syndrome

Exposure of cultured piglet primary neonatal coronary arterial smooth muscle cells to concentrations of ionized Mg2+ ([Mg2+]o (i.e., 0.48, 0.3, 0.15 mM) found in blood of patients presenting with ischemic heart disease and in hypoxic neonates resulted in concentration-dependent elevation in intracellular free Ca2+ ions ([Ca2+]i; the lower the [Mg2+]o, the higher the [Ca2+]i rise. The lowest concentration of [Mg2+]o tested, i.e., 0.15 mM, resulted in a clear rounding-up (i.e., contraction) of many of the coronary smooth muscle cells; reintroduction of normal 1.2 mM [Mg2+]o failed to restore either normal [Ca2+]i or cell shape.

Mg2+ modulates membrane lipids in vascular smooth muscle: a link to atherogenesis

Epidemiological studies associate low dietary magnesium intake with an increased incidence of ischemic heart disease and sudden cardiac death. We have used proton-magnetic resonance (1H-NMR) techniques and Mg2+-selective electrodes to monitor changes in lipid extracts of aortic and cerebrovascular smooth muscle as extracellular ionized magnesium ion concentration ([Mg2+]o) is lowered. We have found that, within the pathophysiological range of Mg2+ concentrations, fatty acid chain length and double bond content are progressively reduced as [Mg2+]o is lowered. In contrast, the plasmalogen content is progressively increased. A concomitant decrease in fatty acid chain length and double bonds indicates oxidation of double bonds resulting in truncation of the fatty acids. A decrease in lipid oxidation in the presence of elevated Mg2+ could contribute to the apparent protective role of increased Mg2+ intake on vascular function in humans.

Role of magnesium in patho-physiological processes and the clinical utility of magnesium ion selective electrodes

Magnesium ions (Mg2+) are pivotal in the transfer, storage and utilization of energy; Mg2+ regulates and catalyzes some 300-odd enzyme systems in mammals. The intracellular level of free Mg2+ ([Mg2+]i) regulates intermediary metabolism, DNA and RNA synthesis and structure, cell growth, reproduction, and membrane structure. Mg2+ has numerous physiological roles among which are control of neuronal activity, cardiac excitability, neuromuscular transmission, muscular contraction, vasomotor tone, blood pressure and peripheral blood flow. Mg2+ modulates and controls cell Ca2+ entry and Ca2+ release from sarcoplasmic and endoplasmic reticular membranes. Since the turn of this century, there has been a steady and progressive decline of dietary Mg intake to where much of the Western World population is ingesting less than an optimum RDA. Geographic regions low in soil and water Mg demonstrate increased cardiovascular morbidity and mortality. Dietary deficiency of Mg2+ results in loss of cellular K+ and gain of cellular Na+ and calcium ions (Ca2+). Blood normally contains Mg2+ bound to proteins, Mg2+ complexed to small anion ligands and free ionized Mg2+ (IMg2+). Most clinical laboratories only now assess the total Mg, which consists of all three Mg fractions. Estimation of the IMg2+ level in serum or plasma by analysis of ultrafiltrates (complexed Mg + IMg2+) is somewhat unsatisfactory, as the methods employed do not distinguish the truly ionized form from Mg2+ bound to organic and inorganic anions. Because the levels of these ligands can vary significantly in numerous pathological states, it is desirable to directly measure the levels of IMg2+ in complex matrices such as whole blood, plasma and serum. Using novel ion selective electrodes (ISE's), we have found that there is virtually no difference in IMg2+, irrespective of whether one samples whole blood, plasma or serum. These data demonstrate that the mean concentration of IMg2+ in blood is about 600 mumoles/litre (0.54-0.65 mmol/L, 95% Cl); 65-72% of total Mg being free or biologically-active Mg2+. Use of the NOVA and KONE ISE's for IMg2+ on plasma and sera from patients with a variety of pathophysiologic and disease syndromes (e.g., long-term renal transplants, liver transplants, during and before cardiac surgery, ischemic heart disease [IHD], headaches, pregnancy, neonatal period, non-insulin dependent diabetes (NIDDM), end-stage renal disease [ESRD], hemodialyse [HEM], and continuous ambulatory peritoneal dialysis (CAPD), hypertension, myocardial infarction [AMI] and after excessive dietary intake of Mg), has revealed interesting data. The results indicate that long-term renal transplant patients, headache, pregnant, NIDDM, ESRD, HEM, CAPD, AMI, hypertensive, and IHD subjects exhibit, on the average significant depression in IMg2+ but not TMg. Use of 31P-NMR spectroscopy on red blood cells, from several of these disease states, to assess free intracellular Mg ([Mg2+]i demonstrates a high correlation (r = 0.5-0.8) between IMg2+ and [Mg2+]i. Increased dietary load of Mg, for only 6 days, in human volunteers, resulted in significant elevations in serum IMg2+ but not TMg. Correlations between the clinical course of several of the above disease syndromes and the fall in IMg2+ and [Mg2+]i were found. The ICa2+/IMg2+ ratio appears, from our data, to be an important guide for signs of peripheral vasoconstriction, ischemia or spasm and possibly atherogenesis. Overall, our data point to important uses for ISE's for IMg2+ in the diagnosis and treatment of disease states.

Predictive value of serum ionized but not total magnesium levels in head injuries

Despite a wealth of recent literature and research on traumatic brain injury, very little has been applicable to diagnosing and treating this syndrome at a tissue level. Part of this problem is the inability to assess rapidly and early in the syndrome the degree or progression of brain injury at a tissue level using simple biochemical analytes. With this in mind, we designed a study in 66 human subjects, who presented with acute blunt head trauma, to determine whether free, ionized serum magnesium (IMg2+) and/or free, ionized serum calcium (ICa2+) levels correlated with the severity of head trauma (HT) and whether any predictive reliable patterns emerge. By using a new ion-selective electrode (ISE) for IMg2+, we have been able to determine IMg2+ and ICa2+ within minutes after sampling in the serum of patients early (1-8 h) after HT. These studies reveal that acute HT is associated with graded deficits (up to 62%, mean = 25%) in serum IMg2+, but not in total serum Mg, which are related to severity of injury based on CT scans and other diagnostic parameters. The greater the degree of injury, the greater the ICa2+/IMg2+ ratio. These ionic findings are compatible with the idea that early ischaemia after head trauma may be important in determining neurological outcome. Our findings provide the first evidence for divalent cation changes in blood after traumatic brain injury, which could be of both diagnostic and prognostic value in patients with traumatic brain injury.

Measurement of free magnesium in blood, serum and plasma with an ion-sensitive electrode

The fraction of total magnesium bound to protein and other substances depends upon the pH. pH-dependency of ionized free magnesium (iMg2+) in serum is expressed by the Siggaard-Andersen equation: iMg2+ (pH) = iMg2+ (7.4) x 10x(7.4 - pH). During preparation of serum or plasma, considerable pH changes occur which have to be corrected on the basis of the above mentioned equation. For pH correction of iMg2+, x < 0.1 has so far been used. However, this is correct only for new Mg(2+)-sensitive electrodes. During the lifetime of Mg2+ electrodes used in the "Microlyte Magnesium" (Kone Instruments, Finland) x increases and x = 0.2 was found to be a suitable approximation for most of the lifetime. By instantaneous iMg2+ measurements in whole blood samples pH changes and the uncertainty of x can be avoided. Dilution of blood by intravenous infusions decreases x nearly proportionally to the decrease of protein concentration in blood. Various methodological influences such as temperature and delay time before centrifugation, storage of serum and venous occlusion were studied. The circadian rhythm of iMg2+ was found to be considerably more pronounced than that of total Mg and was negatively correlated to changes of free fatty acids. To avoid variations of iMg2+ due to circadian changes, blood collection should be carried out between 6 and 10 a.m. The normal range of iMg2+ in blood of 179 healthy subjects was found to be between 0.46 and 0.60 mmol/l and the quotient of free and total Mg between 0.59 and 0.71. The accuracy of "Microlyte Magnesium" (Kone Instruments, Finland) is sufficient in a wide range of iMg2+.