Characterization of a new ion selective electrode for ionized magnesium in whole blood, plasma, serum, and aqueous samples

Does Ionized Magnesium Offer a Different Perspective Exploring the Association between Magnesemia and Targeted Cardiovascular Risk Factors?

Evidence of the association of magnesium (Mg) with arterial stiffness has so far been conflicting. The interplay between hypertension and elevated body mass index (BMI), with hypomagnesemia, instead, has been described in the literature in a more consistent way. Our study aims at revisiting the correlations between blood Mg levels and hemodynamic and body composition parameters in the general population, exploring the sensitivity profile of ionized Mg (Ion-Mg) compared to total Mg (Tot-Mg). We collected data from 755 subjects randomly chosen from a Swiss population previously described and stratified our sample into four equivalent classes according to ionized (whole blood) and total (serum) magnesium. After correcting for age, statistically significant differences emerged between: (i) Tot-Mg ≤ 0.70 and 0.81 ≤ Tot-Mg ≤ 0.90 for cf-PWV (p = 0.039); (ii) Tot-Mg ≤ 0.70 and Tot-Mg ≥ 0.91 for o-PWV (p = 0.046). We also found a statistically significant difference among groups of Ion-Mg values for the 24 h extremes of systolic blood pressure (p = 0.048) and among groups of Tot-Mg for BMI (p = 0.050). Females showed significantly lower levels of total magnesium (p = 0.035) and ionized magnesium (p < 0.001) than males. The overall agreement between magnesium analysis methods was 64% (95%CI: 60.8−67.7%). Our results confirm that Ion-Mg compared with Tot-Mg offers a different profile in detecting both correlations with hemodynamic and body composition parameters and dysmagnesemias. Lower levels of magnesium were associated with worse arterial aging parameters, larger 24 h blood pressure excursions, and higher BMI. Ion-Mg was superior in detecting the correlation with blood pressure only. Considering Ion-Mg as a more specific marker of the magnesium status, and the partially contradictory results of our explorative cross-sectional study, to avoid confounding factors and misinterpretations, ionized magnesium should be used as reference in future studies.

Measurement of Serum Ionized Magnesium in Capd Patients

Objective

To evaluate the magnesium status of continuous ambulatory peritoneal dialysis (CAPD) patients using a new method for assessing the level of the ionized fraction a serume magnesiumy.

Design

Serum ionized magnesium was measured in CAPD patients using the ion-selective electrode for Mg2+.

Setting

The Dialysis Unit of Tampere University Hospital.

Patients

Twenty -six patients on CAPD (age: 21 -81 years, mean 54 ± 16 years; duration of CAPD: 3 -52 months, mean 13 months), and 26 sex and age-matched healthy controls.

Results

Both serum ionized magnesium (0.73 ± 0.11 mmol/L vs 0.56 ± 0.07 mmol/L, p < 0.001) and total magnesium (1.11 ± 0.22 vs 0.81 ± 0.08 mmol/L, p < 0.01) were higher in CAPD patients than in sex and agematched controls. The ionized magnesium fraction of total magnesium was slightly lower in dialysis patients in spite of the fact that 16/26 patients had serum albumin less than 36 g/L. Hypermagnesemia (mean serum ionized magnesium 0.78± 0.10 mmol/L) was observed in the 13 of 26 patients with 0.75 mmol/L Mg2+ dialysate; those with lower magnesium dialysate (Mg2+ 0.50 mmol/L in 10/26 and Mg2+ 0.25 mmol/L in 3/26) had mean serum ionized magnesium at the upper normal margin (0.69 ± 0.10 mmol/L).

Conclusion

In CAPD patients with Mg2+ 0.5 0.75 mmol/L in their dialysis fluid, both serum ionized and total magnesium concentrations were higher but the ionized/total magnesium ratio was lower than in healthy control subjects. Use of ion-selective electrodes to measure ionized magnesium may be a more useful methodology than measuring total magnesium in the evaluation of magnesium status of CAPD patients, because it is not infuenced by hypoalbuminemia or increased complexed fraction of magnesium often present in dialysis patients.

Circulating Ionized Magnesium: Comparisons with Circulating Total Magnesium and the Response to Magnesium Supplementation in a Randomized Controlled Trial

Ionized Mg (iMg) is considered the biologically active fraction of circulating total Mg (tMg). It is possible that iMg may be a more physiologically relevant marker than tMg. Using data from a double-blind pilot randomized controlled trial, we tested (1) whether oral Mg supplementation will increase iMg concentrations compared with placebo and (2) the relationship between iMg and tMg at baseline. Additionally, we evaluated the agreement between iMg measured in fresh whole blood versus stored samples. A total of fifty-nine participants were randomized 1:1 to oral Mg supplementation (400 mg/day, Mg Oxide) or placebo for 10 weeks. Fasting blood samples were obtained at baseline and follow-up. The analysis used linear regression and an intent-to-treat approach. Participants were generally healthy, the mean age was 62, and 73% were female. The baseline iMg and tMg were modestly and positively associated (r = 0.50). The ratio of baseline iMg to tMg was 64%. The mean supplement effect on iMg was 0.03 mmol/L (95% CI:0.01, 0.05) for Mg supplementation versus placebo. The supplement effect on iMg was not statistically significantly different according to baseline iMg status (above/below median). Compared to fresh blood, iMg was consistently higher in refrigerated and frozen samples by 0.14 and 0.20 mmol/L, respectively. In this relatively healthy adult population, Mg supplementation over 10 weeks resulted in increased iMg concentrations. Whether iMg is a more appropriate measure of Mg status than tMg, and the public health or clinical utility of measuring iMg remains to be determined.

Total and ionized serum magnesium and calcium levels during magnesium sulfate administration for preterm labor

Objective

This study aimed to estimate the association between total and ionized magnesium, and the changes in serum magnesium and calcium levels in patients with preterm labor during magnesium sulfate (MgSO₄) administration.

Methods

The study population included 64 women who were candidates for intravenous MgSO₄ treatment for preterm labor. Serial blood samples were taken and measured total magnesium (T-Mg), ionized magnesium (I-Mg), total calcium (T-Ca), and ionized calcium (I-Ca) levels every one-week interval (1st, 2nd, 3rd).

Results

There was no significant difference in T-Mg and I-Mg levels during MgSO₄ administration (P>0.05). There was no significant difference in T-Ca and I-Ca levels during MgSO₄ administration (P>0.05). Compared before and after administration of MgSO₄, T-Mg and I-Mg levels and T-Ca levels were changed allow statistically significant (P<0.05). But, there was no significant difference in the I-Ca serum levels before and after MgSO₄ administration (P=0.495). The I-Mg levels for patients with adverse effect were higher than other group but did not reach statistical significance (P>0.05). There was significant correlation between levels of I-Mg and T-Mg (I-Mg=0.395×T-Mg+0.144, P<0.01).

Conclusion

There were no significant differences in serum Mg and Ca levels during MgSO₄ administration for preterm labor. Compared to the before and after administration of MgSO₄, only I-Ca levels were not substantially changed. There are significant correlations between I-Mg and T-Mg levels during administration of MgSO₄ and I-Mg level seemed to have more correlation with adverse effect than T-Mg.

Reduced Mortality in Maintenance Haemodialysis Patients on High versus Low Dialysate Magnesium: A Pilot Study

Background: Although low magnesium levels have been associated with an increased mortality in dialysis patients, they are kept low by routinely-used dialysates containing 0.50 mmol/L magnesium. Thus, we investigated the impact of a higher dialysate magnesium concentration on mortality. Methods: 25 patients on high dialysate magnesium (HDM) of 0.75 mmol/L were 1:2 matched to 50 patients on low dialysate magnesium (LDM) of 0.50 mmol/L and followed up for 3 years with regards to all-cause and cardiovascular mortality. Patients were matched according to age, gender, a modified version of the Charlson Comorbidity Index (CCI), and smoking status. Results: During the follow-up period, five patients died in the HDM and 18 patients in the LDM group. Patients in the HDM group had significantly higher ionized serum magnesium levels than matched controls (0.64 ± 0.12 mmol/L vs. 0.57 ± 0.10 mmol/L, p = 0.034). Log rank test showed no difference between treatment groups for all-cause mortality. After adjustment for age and CCI, Cox proportional hazards regression showed that HDM independently predicted a 65% risk reduction for all-cause mortality (hazard ratio 0.35, 95% confidence interval [CI]: 0.13, 0.97). Estimated 3-year probability of death from a cardiovascular event was 14.5% (95% CI: 7.9, 25.8) in the LDM group vs. 0% in the HDM group. Log rank test found a significant group difference for cardiovascular mortality (χ² = 4.15, p = 0.042). Conclusions: Our data suggests that there might be a beneficial effect of an increased dialysate magnesium on cardiovascular mortality in chronic dialysis patients.

The Importance of Magnesium in the Human Body: A Systematic Literature Review

Magnesium, the second and fourth most abundant cation in the intracellular compartment and whole body, respectively, is of great physiologic importance. Magnesium exists as bound and free ionized forms depending on temperature, pH, ionic strength, and competing ions. Free magnesium participates in many biochemical processes and is most commonly measured by ion-selective electrode. This analytical approach is problematic because complete selectivity is not possible due to competition with other ions, i.e., calcium, and pH interference. Unfortunately, many studies have focused on measurement of total magnesium rather than its free bioactive form making it difficult to correlate to disease states. This systematic literature review presents current analytical challenges in obtaining accurate and reproducible test results for magnesium.

Umbilical artery pH may be a possible confounder for neonatal adverse outcomes in preterm infants exposed to antenatal magnesium

OBJECTIVES

To determine the normal range of ionized magnesium (IMg) levels in cord blood during preterm gestation and to investigate whether antenatal Mg administration affects neonatal intraventricular hemorrhage (IVH) or patent ductus arteriosus (PDA).

METHODS

In this retrospective case-control study, we reviewed 118 pregnant women with antenatal Mg administration and their infants after they gave birth at one tertiary care center between January 2006 and December 2010. Thirty-seven cases with IVH and/or PDA were compared to 81 controls by multiple logistic regression analysis. The normal range of IMg levels was determined by another 79 subjects without any tocolytic agents and possible confounders. Perinatal and neonatal characteristics were then compared between three groups divided by the IMg levels in cord serum.

RESULTS

The normal range of IMg levels in cord blood was determined to be 0.47 ± 0.07 mmol/L, regardless of gestational weeks. IMg level in cord serum could not be a risk factor for IVH or PDA. Elevation of IMg level in cord blood resulted in an increased incidence of IVH and a decreased incidence of PDA, but not significantly. IMg level in cord blood was inversely correlated with umbilical artery pH (p = 0.067).

CONCLUSIONS

There was no significant relationship between the IMg levels in cord serum and neonatal IVH and PDA. Umbilical artery pH may be a possible confounder.

Densitometric and biochemical values of broiler tibias at different ages

The objective of this experiment was to determine the normal values of bone radiographic density (BRD) by using the optical densitometry in radiographic images and the biochemical values represented by serum calcium, ash percentage, and minerals (calcium, phosphorus, and magnesium) from tibia ash of Cobb broilers at 8, 22, and 43 d of age. A total of 14 broilers were used for densitometric analysis, and 15 were used for biochemical dosages. The BRD values increased (P < 0.05) with age and in all tibia regions (proximal epiphysis, diaphysis, and distal epiphysis), concluding that growth was a determinative factor for bone performance, demanding a higher BRD during broiler development. Tibia proximal epiphysis presented higher BRD values in relation to the other bone regions (P < 0.05), as a result of a possible biomechanical adaptation to ligaments and tension of the muscle tendons at this region, allowing the support of the muscle mass increase. The serum calcium values were kept constant, as a result of the appropriate nutritional levels of the diet that supported the animal homeostasis. The bone ash and mineral percentage increased (P < 0.05) at 22 d of age, due to the higher mineral requirement in this age. The correlation between bone densitometry and the invasive techniques showed that the bone densitometry can substitute the determination of mineral percentage in the ash. This experiment presented normal values of the noninvasive and invasive methods more used in aviculture, allowing us to compare, subsequently, pathological and physiological values or results of broilers fed with different diets.

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.

Cerebral spinal fluid and serum ionized magnesium and calcium levels in preeclamptic women during administration of magnesium sulfate

OBJECTIVE

To study the distribution of ionized and total magnesium (Mg) in serum and cerebral spinal fluid (CSF) in preeclamptic women receiving MgSO(4) and how this treatment affects the ionized calcium (Ca(2+)) and ionized Ca:Mg ratios compared with healthy nonpregnant women and pregnant control women (HP).

DESIGN

Controlled clinical study.

SETTING

An academic medical center.

PATIENT(S)

African-American women older than 20 and less than 35 years. The pregnant preeclamptic study and pregnant control groups each consisted of 16 women; the nonpregnant group consisted of 10 subjects.

INTERVENTION(S)

The preeclamptic women received a 6-g bolus of MgSO(4) IV started at least 4.5 hours before delivery during 15-20 minutes, then 2 g/h baseline.

MAIN OUTCOME MEASURE(S)

The CSF and serum levels of Ca(2+) and Mg(2+) and total Mg were measured in all three groups of women. The Ca(2+):Mg(2+) ratios were determined. Physiologic monitoring was done and recorded every 4 hours where appropriate. Bloods were drawn every 6 hours for complete blood count, metabolic panel, lactate dehydrogenase, uric acid, and electrolytes. Serum pH, total Mg, Apgar scores, and general health of the infants born to preeclamptic mothers given MgSO(4) were followed.

RESULT(S)

The HP showed a reduction in mean serum ionized and total Mg, increase in ionized Ca, and a large increase in Ca(2+):Mg(2+) ratios compared with healthy nonpregnant women. Although the CSF ionized and total Mg and Ca(2+):Mg(2+) ratios were not altered with MgSO(4) treatment in the preeclamptic women receiving MgSO(4), the mean serum Mg values increased 3-fold. All infants were full-term, regardless of MgSO(4) treatment, and normal with respect to birth weight, Apgar scores, blood pH, total Mg, and neurologic scores.

CONCLUSION(S)

The data indicate that there is a direct relationship between the serum and CSF Ca(2+):Mg(2+) ratios in HP and this ratio may be crucial in preventing vascular and neurologic complications in preeclampsia-eclampsia.

Magnesium metabolism in hypertension and type 2 diabetes mellitus

The increasing evidence for the clinical relevance of altered magnesium metabolism to states of altered insulin resistance confirms the role of magnesium deficit as a possible underlying common mechanism of the "insulin resistance" of hypertension and altered glucose tolerance. The pioneer work of Lawrence M. Resnick and his group using the cellular ion-based approach that we are only partially presenting here has consistently contributed to the progress of the field, demonstrating (a) the critical importance of magnesium metabolism in regulating insulin sensitivity as well as vascular tone, and blood-pressure homeostasis; (b) that magnesium deficiency, defined on the basis of intracellular free magnesium levels, and or serum ionized magnesium is a common feature of both diabetic and hypertensive states as well as various other cardiovascular and metabolic processes and aging; (c) the ability of environmental factors such as dietary nutrient-sugar and mineral content to alter the set point of steady-state cell ion activity; and (d) that magnesium supplementation is indicated in conditions associated with magnesium deficit although well-designed therapeutic trials of magnesium in essential hypertension and type 2 diabetes mellitus are needed in the near future.

A peculiar form of epilepsy induced by crying in infancy

We describe a peculiar form of epilepsy following prolonged and vigorous bouts of crying in infancy which was misdiagnosed as breath holding spells. Three patients with crying-induced epilepsy had the following characteristics. The patients were born after uncomplicated pregnancy, labor, and delivery. The seizures presented between the ages of 10 and 18 months, the patients had normal development and cranial MRIs, no past or family histories of epilepsy or cardiac disease, and developed generalized tonic clonic seizures only following crying after a sudden, unexpected and mildly unpleasant stimulus. The seizures usually lasted no longer than 1 min and their EEG showed focal spikes in interictal states and generalized spikes in ictal states. The seizures were well controlled with valproate sodium. This peculiar form of epilepsy may be a benign age-dependent reflex epilepsy in infancy.

Pilot study to determine the hemodynamic safety and feasibility of magnesium sulfate infusion in children with severe traumatic brain injury

OBJECTIVE

Magnesium sulfate is neuroprotective in preclinical models, but there are limited safety data regarding its clinical use for pediatric traumatic brain injury. We conducted a pilot study in children with severe traumatic brain injury to a) examine if magnesium sulfate decreases mean arterial pressure, decreases cerebral perfusion pressure, increases intracranial pressure, or adversely effects cardiac conduction; and b) determine the feasibility of a multiple-center trial of magnesium sulfate.

DESIGN

Double-blinded, placebo-controlled, randomized pilot trial with repeated measurement of hemodynamic variables.

SETTING

Two pediatric trauma centers.

PATIENTS

Six children (3 months to 18 yrs) with severe traumatic brain injury.

INTERVENTIONS

: Magnesium sulfate (50 mg/kg) bolus followed by (8.3 mg/kg/hr) infusion for 24 hr vs. equivolume placebo.

MEASUREMENTS AND MAIN RESULTS

We screened 96 patients with severe traumatic brain injury during 24 months; 20 were eligible for enrollment, six provided informed consent, four received magnesium sulfate, and two received placebo. Before and after study drug infusion, we repeatedly measured blood ionized magnesium concentration, mean arterial pressure, cerebral perfusion pressure, intracranial pressure, heart rate, and corrected QT interval. Mean age (7.9 yrs), mean highest Glasgow Coma Scale score (6), gender (33% boys), inflicted injury rate (17%), and case mortality rate (17%) did not differ between those enrolled and those not enrolled. Compared with baseline, magnesium sulfate did not change cerebral perfusion pressure, intracranial pressure, heart rate, or corrected QT interval. Mean arterial pressure was unchanged until the late phase of magnesium sulfate infusion, when mean arterial pressure rose (82 +/- 5 vs. 93 +/- 6 mm Hg, p < .05). Sixty-four percent of corrected QT interval determinations obtained in the first 6 days after injury exceeded 440 msecs; 12% were >600 msecs.

CONCLUSIONS

In children with severe traumatic brain injury, magnesium sulfate administration did not decrease mean arterial pressure or cerebral perfusion pressure or adversely effect cardiac conduction. Our data suggest that enrollment of brain-injured children in a therapeutic trial remains challenging. These results provide information important for clinical trials of magnesium sulfate in children with severe traumatic brain injury.

Secondary hyperparathyroidism and hypovitaminosis D in African-Americans with decompensated heart failure

OBJECTIVE

We previously noted secondary hyperparathyroidism (SHPT) in African-American patients hospitalized during February, 2005 with either untreated or treated congestive heart failure (CHF) due to ischemic or idiopathic cardiomyopathy. Herein, we hypothesized that housebound African-American patients hospitalized during the period of June 1 through August 31, 2005, with CHF would have SHPT and hypovitaminosis D.

METHODS

Twenty-five African-American patients with an ejection fraction (EF) less than 35% due to ischemic or dilated (idiopathic) cardiomyopathy were monitored: 20 were hospitalized with CHF, stratified on historical grounds as of 4 weeks' or longer duration or of 1 to 2 weeks' duration in 11 and 9 patients, respectively, despite medical care that included furosemide; serum parathyroid hormone (PTH) and 25(OH)D at the time of admission in these patients were compared to five asymptomatic outpatients seen during the summer with stable, compensated failure.

RESULTS

Serum PTH was elevated (127 +/- 13; 82-243 pg/mL) in all patients with CHF of 4 weeks' or longer duration (normal, 12-65 pg/mL) and was elevated in three of nine patients (59 +/- 8; 18-99 pg/mL) with CHF of 1 to 2 weeks' duration. Ionized hypocalcemia (1.09 +/- 0.03 and 1.08 +/- 0.02 mmol/L; normal, 1.12-1.30) and hypomagnesemia (0.47 +/- 0.02 and 0.46 +/- 0.03 mmol/L; normal, 0.53-0.67) were respectively found in long- or short-duration CHF. No compensated patient had elevated PTH (42 +/- 5; 17-53). Hypovitaminosis D (< or =30 ng/mL) was universally present in patients with CHF of 4 weeks' or longer duration (15.1 +/- 1.4; 7.0-23.8 ng/mL) and was also prevalent in the other groups (20.3 +/- 5.1, 7.0-54.1 ng/mL in CHF of 1 to 2 weeks' duration and 23.1 +/- 4.9; 17.2-42.7 ng/mL in compensated failure).

CONCLUSIONS

In African-American patients with CHF, hypovitaminosis D, aldosteronism, and loop diuretic treatment each exaggerate Ca and Mg losses to stress a fragile Ca balance leading to ionized hypocalcemia and hypomagnesemia with SHPT.

Serum ionized magnesium during magnesium sulfate administration for preterm labor and preeclampsia

OBJECTIVE

The purpose of this study is to estimate the relations between ionized and total Mg levels during MgSO4 administration in patients with preterm labor and preeclampsia.

METHODS

Forty-three pregnant patients who were candidates for MgSO4 were studied (preterm labor, 27; preeclampsia, 16). The administration method was intravenous injection of MgSO4 4 g over 30 min followed by 1-2 g/h. Ionized Mg was measured by the selective ion electrode method at bedside, and compared it with total Mg levels.

RESULTS

Significant correlation was existed between levels of ionized and total Mg throughout therapy for both preterm labor (ionized Mg=0.19 x total Mg+0.19; r=0.61, p<0.001) and preeclampsia (ionized Mg=0.20 x total Mg+0.14; r=0.60, p<0.001).

CONCLUSION

There are correlations between ionized and total Mg levels during administration of MgSO4 for both preterm labor and preeclampsia.

Evaluation of an electrolyte analyser for measurement of concentrations of ionized calcium and magnesium in cats

The goal of this study was to evaluate the Nova CRT 8 electrolyte analyser for determination of concentrations of ionized calcium (Ca(i)) and magnesium (Mg(i)) in cats, to determine the effects of sample handling and storage and to establish reference ranges. The precision and analytical accuracy of the Nova CRT 8 analyser were good. The concentrations of Ca(i) and Mg(i) were significantly lower in aerobically handled serum samples than in those handled anaerobically. The concentrations of Ca(i) and Mg(i) differed significantly among whole blood, plasma and serum. In anaerobically handled serum, the concentration of Ca(i) was stable for 8 h at 22 degrees C, for 5 days at 4 degrees C and for 1 week at -20 degrees C. The concentration of Mg(i) was stable for 4 h at 22 degrees C but for less than 24 h at 4 degrees C and for less than 1 week at -20 degrees C. In serum from 36 cats, the reference ranges were 1.20-1.35 mmol/L for Ca(i) and 0.47-0.59 mmol/L for Mg(i). The Nova CRT 8 electrolyte analyser is suitable for determination of Ca(i) and Mg(i) concentrations in cats. Anaerobically handled serum samples are recommended and, stored at room temperature, they yield accurate results when analysed within 4 h.

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.

Studies on cerebrospinal fluid ionized calcium and magnesium concentrations in convulsive children

BACKGROUND

The concentrations of ionized calcium (iCa) and ionized magnesium (iMg) were measured in the cerebrospinal fluid (CSF) of convulsive and non-convulsive children, to investigate the relationship between seizure manifestation and CSF iCa and iMg concentrations. Standard concentrations of CSF iCa and iMg were also established.

METHODS

CSF samples from 23 patients, ages 0-15 years, with various forms of seizures and 26 age-matched non-convulsive children were collected by lumbar puncture. CSF was obtained anaerobically and the concentrations of CSF iCa and iMg were measured with an electolyte analyzer (Stat Profile Ultra M1, NOVA, USA) immediately after the lumbar puncture.

RESULTS

The concentrations of CSF iCa were significantly higher in non-convulsive children younger than 11 months old compared with children older than 12 months. The concentrations of CSF iMg in non-convulsive children did not differ significantly with aging. The concentrations of CSF iCa in convulsive children did not differ significantly from the concentrations of non-convulsive children. The concentrations of CSF iMg in convulsive children were significantly lower than in non-convulsive children.

CONCLUSION

These results suggest that seizure manifestation is related to age-dependent changes in iCa and decreased iMg in the developing brain.

Evaluation of plasma ionized magnesium levels in neonatal hyperbilirubinemia

Plasma levels of ionized magnesium (IMg) measured by ion-selective electrode were investigated in neonatal hyperbilirubinemia by comparing the newborns with (> or =205 microM) and without (<205 microM) significant hyperbilirubinemia (groups of severe and moderate hyperbilirubinemia, respectively). Serum bilirubin, plasma IMg, and ionized calcium (ICa) levels were determined in 165 healthy term newborns with nonhemolytic indirect hyperbilirubinemia during the first 10 d of life. Mean serum bilirubin, plasma IMg, and ICa levels were 200.1 +/- 126.5 microM, 0.54 +/- 0.12 mM, and 1.15 +/- 0.12 mM, respectively, in 165 newborns whose mean postnatal age was 156.1 +/- 46.5 h, and there was a significant positive correlation between the mean serum bilirubin and plasma IMg levels (r = 0.535, p < 0.001). Serum bilirubin levels (304.4 +/- 83.8 microM versus 94.1 +/- 54.7 microM) and plasma IMg levels (0.6 +/- 0.12 mM versus 0.49 +/- 0.1 mM) were significantly higher and plasma ICa levels (1.13 +/- 0.12 mM versus 1.18 +/- 0.12 mM) were significantly lower in the group of severe hyperbilirubinemia (n = 83) when compared with the group with moderate hyperbilirubinemia (n = 82). Seventeen of the 83 cases of severe hyperbilirubinemia had IMg levels above the normal range (> or =0.69 mM), whereas none of the 82 cases of moderate hyperbilirubinemia had elevated IMg levels. Fifteen of the 17 with high IMg levels had bilirubin levels >290 microM. Results of the present study suggest that increase in plasma IMg may be due to extracellular movement of Mg, a principally intracellular ion, resulting from generalized cellular injury including neurons and erythrocytes. Considering neuroprotective functions and beneficial effects of Mg ion in improving neurologic outcome, we also may speculate the possibility of a neuroprotective role or a compensatory mechanism in IMg increase against emerging toxicity risk of increasing serum bilirubin levels.

Pharmacokinetics of ionized versus total magnesium in subjects with preterm labor and preeclampsia

OBJECTIVE

Intravenous magnesium sulfate is widely used in obstetrics for the treatment of both preterm labor and preeclampsia. Although therapeutic levels of total magnesium have been proposed, the levels remain controversial. Because the active form of magnesium is the free or ionized form, it is essential to determine whether ionized magnesium and total magnesium levels are highly correlated in vivo. We sought to examine the correlation between ionized magnesium and total magnesium under basal and therapeutic conditions and to define the initiation and elimination pharmacokinetics of both forms during intravenous magnesium sulfate infusion.

STUDY DESIGN

Twenty-four singleton pregnant patients who were candidates for magnesium sulfate were studied (preterm labor, 15; preeclampsia, 9). Serial blood samples were taken before the magnesium sulfate infusion, during the first 4 hours after the initiation of magnesium sulfate infusion and for 4 hours after the discontinuation of the infusion.

RESULTS

Baseline levels of total magnesium and ionized magnesium were not different between patients with preterm labor and with preeclampsia. Among patients with preeclampsia, although not patients with preterm labor, the initial apparent volume of distribution was significantly smaller for total magnesium than for ionized magnesium (16,397 +/- 1441 vs 23,856 +/- 2745 mL, respectively; P =.03), and the elimination half-life was greater for total magnesium as compared to ionized magnesium (707 +/- 160 vs 313 +/- 29 minutes;P <.05). Linear regression analysis demonstrated a lack of correlation between ionized magnesium and total magnesium during the pretreatment period and during the steady state infusion for both preterm labor and preeclampsia.

CONCLUSION

The measurement of total magnesium may not be adequate for the titration of therapeutic magnesium infusions in patients with preeclampsia or preterm labor because of the lack of correlation between total magnesium and the physiologically active ionized magnesium. Further studies may determine whether the measurement of ionized magnesium is a superior method for following the adequacy and safety of the treatment of preeclampsia and preterm labor.

Serum ionized magnesium levels and serum ionized calcium/ionized magnesium ratios in women with menstrual migraine

OBJECTIVE

It has been suggested that magnesium deficiency may play an important role in menstrual migraine and that the serum ionized calcium (ICa2+)/ionized magnesium (IMg2+) ratio is important in migraine headache. Studies were designed to test these hypotheses.

DESIGN

We prospectively evaluated 270 women seen at a headache clinic and in 61 women with menstrual migraine measured IMg2+, total magnesium, and ICa2+ levels so as to calculate the ICa2+/IMg2+ ratio.

RESULTS

The incidences of IMg2+ deficiency were 45% during menstrual attacks, 15% during nonmenstrual attacks, 14% during menstruation without a migraine, and 15% between menstruations and between migraine attacks. The serum ICa2+ levels were within our reference range, but the ICa2+/IMg2+ ratio was elevated (P<.01) in menstrual migraine.

CONCLUSIONS

The high incidence of IMg2+ deficiency and the elevated ICa2+/IMg2+ ratio during menstrual migraine confirm previous suggestions of a possible role for magnesium deficiency in the development of menstrual migraine.

The effects of magnesium supplementation on exercise performance

PURPOSE

To determine the effects of magnesium (Mg2+) supplementation on performance and recovery in physically active women using the sensitive and recently advanced measure of ionic Mg2+ (iMg).

METHODS

Participants (N = 121) were screened for [iMg] in plasma, with 44 (36.4%) exhibiting [iMg] below the normal range of 0.53-0.67 mmol.L-1 (4). Thirty-two subjects (21 +/- 3 yr) representing a broad range of [iMg] (0.54 +/- 0.04 mmol.L-1) completed the main 14-wk study. At baseline, participants submitted to a resting blood pressure measurement, and they completed both an anaerobic treadmill test and an incremental (aerobic) treadmill test. For the latter, values for workload, oxygen uptake, and heart rate were obtained at both anaerobic threshold and maximal effort. Blood samples for iMg, total serum Mg2+ (TMg), erythrocyte Mg2+ (EMg), Ca2+, K+, Na+, hemoglobin, hematocrit, lactate, and glucose were also collected pretest, and 4, 10, 30 min, and 24 h posttest. Subjects received 212 mg.d-1 Mg oxide or placebo in a double-blind fashion and were retested after 4 wk. After a 6-wk washout period, the testing was repeated with a treatment crossover.

RESULTS

Ionic Mg2+ increased with Mg2+ treatment versus placebo (P < 0.05); however, performance and recovery indices were not significantly affected.

CONCLUSION

Four weeks of 212 mg.d-1 Mg oxide supplementation improves resting [iMg] levels but not performance or recovery in physically active women.

The effects of magnesium supplementation on exercise performance

OBJECTIVES

Magnesium (Mg) status, although difficult to assess, is suspected to be marginal in many individuals, especially athletes, and this has led to the common use of Mg supplements. The purpose of this article is to critique research that has addressed Mg supplementation in athletes.

DATA SOURCES

The primary database was Medline, which was searched for English articles from 1966 to June 1999 using the words "magnesium" and "supplementation."

STUDY SELECTION

Only experimental studies dealing with human subjects, Mg supplementation, and exercise performance were critiqued (n = 12).

DATA EXTRACTION

Quality of critiqued articles was based on 1) use of cross-over designs, 2) how and if Mg status was assessed, 3) whether treatment was solely Mg supplementation, 4) duration of supplementation, 5) subject number, and 6) degree of experimental control. Articles were classified into "no effect" and "positive effect," and also were examined in regard to the type of performance outcome (strength, anaerobic-lactacid, and aerobic).

DATA SYNTHESIS

Mg is a cofactor to over 325 enzymatic reactions, and a deficiency of the mineral therefore has many physiological and exercise performance implications. Low dietary intakes, as found in many female athletes, coupled with increased urinary losses with exercise, may eventually lead to an Mg deficiency. Strength of evidence favors those studies finding no effect of Mg supplementation, regardless of whether the performance outcome was strength, anaerobic-lactacid, or aerobic. Analysis was confounded due to: 1) variable exercise modes, intensities, and durations, 2) variable training states and ages of subjects, 3) subject selection favoring males and gender differences has not been probed, 4) Mg dosage has ranged from 1 day to 3 months and from 116 mg/day to 500 mg/day, 5) multivitamins/minerals have been ingested with the Mg, 6) with one exception, Mg status was either not reported or reliant on total Mg (TMg), 7) lack of a cross-over design, 8) only one study made note of controlling exercise prior to exercise testing and blood assay, and 9) typical Mg intake measured was only measured in three of the studies.

CONCLUSIONS

Most evidence indicates no effect of Mg supplementation on performance (strength, anaerobic-lactacid, and aerobic). When only peak treadmill speed during a VO2 max test is examined, the strength of evidence is equivocal. Trained subjects appear to benefit less than untrained subjects, but this observation requires further study. Little research has focused on physically active females who may be at the highest risk for Mg deficiency. Research has been confounded by numerous factors.

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.

Alterations in ionized and total blood magnesium after experimental traumatic brain injury: relationship to neurobehavioral outcome and neuroprotective efficacy of magnesium chloride

Experimental evidence suggests that magnesium plays a role in the pathophysiological sequelae of brain injury. The present study examined the variation of blood ionized and total magnesium, as well as potassium, sodium, and ionized calcium, after experimental fluid percussion brain injury in rats. Blood ionized magnesium concentration significantly declined from 0.45 +/- 0.02 to 0.32 +/- 0.02 mM by 30 min postinjury and stayed depressed for the 24-h study period in vehicle-treated rats. Blood total magnesium concentration was 0.59 +/- 0.01 mM and remained stable over time in brain-injured vehicle-treated animals. When magnesium chloride (125 micromol/rat) was administered 1 h postinjury, ionized magnesium levels were restored by 2 h postinjury and remained at normal values up to 24 h following brain trauma. Magnesium treatment also significantly reduced posttraumatic neuromotor impairments 1 and 2 weeks after the insult, but failed to attenuate spatial learning deficits. A significant positive and linear correlation could be established between ionized magnesium levels measured 24 h postinjury and neuromotor outcome at 1 and 2 weeks. We conclude that acute ionized magnesium measurement may be a predictor of long-term neurobehavioral outcome following head injury and that delayed administration of magnesium chloride can restore blood magnesium concentration and attenuate neurological motor deficits in brain-injured rats.

Serum ionized magnesium and calcium in women after menopause: inverse relation of estrogen with ionized magnesium

OBJECTIVE

To study the serum concentrations of the sex steroid hormones and free divalent cations Mg2+ and Ca2+ in healthy women at or past menopause and to compare them with the serum concentrations of healthy, cycling women of child-bearing age at different stages of the menstrual cycle.

DESIGN

Controlled clinical study.

SETTING

An academic medical center.

PATIENT(S)

Women of varying age and duration of menopause, and healthy, cycling women.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Serum levels of the sex steroids (estrogen, progesterone, and testosterone) and of Ca2+ and Mg2+ were measured in menopausal and postmenopausal women, and in healthy, cycling women at five different stages of the menstrual cycle.

RESULT(S)

The Mg2+ and total Mg levels of the postmenopausal women were inversely related to the serum level of estrogen and were similar to the levels present during the early follicular phase of healthy women of child-bearing age. The Ca2+ level was unrelated to the sex steroid hormones present, but it was increased compared with that of younger women in both the follicular phase and the luteal phase.

CONCLUSION(S)

Serum levels of Mg2+ and total Mg were inversely correlated with the estrogen concentration in menopausal women. Serum levels of Ca2+ were significantly elevated in menopausal women compared with younger women, but the ratio of Ca2+ to Mg2+, a measure of cardiovascular problems, was not elevated in the postmenopausal women.

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.

Sex steroid hormones modulate serum ionized magnesium and calcium levels throughout the menstrual cycle in women

OBJECTIVE

To determine the serum concentrations of the sex steroid hormones with respect to the concentrations of the biologically active fractions of magnesium and calcium during the different phases of the menstrual cycle.

DESIGN

Controlled clinical study.

SETTING

An academic research environment.

PATIENT(S)

Six parous and four nulliparous healthy cycling female volunteers.

MAIN OUTCOME MEASURE(S)

Concentrations of the sex steroid hormones estrogen, progesterone, and testosterone as well as the ionized Ca and Mg levels were measured in the serum of normal cycling women during five different stages: the menstrual, early follicular, late follicular, ovulatory (ovulatory/early luteal), and luteal phases.

RESULT(S)

In each woman, there was a comparatively high ionized Mg level coincident with the early follicular phase, a statistically significant decrease in ionized Mg around the time of ovulation, a significant decrease in ionized and total Mg when the serum progesterone concentration peaked, and a significant increase in the serum Ca2+/Mg2+ ratio at both the ovulatory and luteal phases. In addition, a decrease in ionized Mg was found with increased testosterone levels.

CONCLUSION(S)

Healthy women of reproductive age demonstrate recurring cycling of ionized Mg and cyclic alterations in the ionized Ca to Mg ratio in their serum. The changes in serum concentrations of these important physiologically active cations, in the range at which they occur, can affect such entities as the vasculature, synaptic transmission, and excitation-secretion coupling and thus can produce the well-known premenstrual syndromes during the luteal phase in women who are somewhat deficient in Mg or in those who have an unusually increased Ca2+/Mg2+ ratio.

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.

Low levels of serum ionized magnesium are found in patients early after stroke which result in rapid elevation in cytosolic free calcium and spasm in cerebral vascular muscle cells

Ninety-eight patients admitted to the emergency rooms of three urban hospitals with a diagnosis of either ischemic stroke or hemorrhagic stroke exhibited early and significant deficits in serum ionized Mg2+ (IMg2+), but not total Mg, as measured with a unique Mg2+-sensitive ion-selective electrode. Twenty-five percent of these stroke patients exhibited >65% reductions in the mean serum IMg2+ found in normal healthy human volunteers or patients admitted for minor bruises, cuts or deep lacerations. The stroke patients also demonstrated significant elevation in the serum ionized Ca2+ (ICa2+)/IMg2+ ratio, a sign of increased vascular tone and cerebrovasospasm. Exposure of primary cultured canine cerebral vascular smooth muscle cells to the low concentrations of IMg2+ found in the stroke patients, e.g. 0.30-0.48 mM, resulted in rapid and marked elevations in cytosolic free calcium ions ([Ca2+]i) as measured with the fluorescent probe, fura-2, and digital image analysis. Coincident with the rise in [Ca2+]i, many of the cerebral vascular cells went into spasm. Reintroduction of normal extracellular Mg2+ ion concentrations failed to either lower the [Ca2+]i overload or reverse the rounding-up of the cerebral vascular cells. These results suggest that changes in Mg2+ metabolism play important roles in stroke syndromes and in the etiology of cerebrovasospasm associated with cerebral hemorrhage.