Since magnesium is mainly an intracellular ion, measurement of serum total magnesium is an inaccurate index of intracellular or total magnesium stores. This means that although your serum levels are being maintained within normal limits, there could be a deficiency in tissues that is not being detected.
The different types of testing are described below.
Total Red Cell Magnesium
Although this test is becoming more available and the results are less variable than serum measurements, it may not adequately reflect total body magnesium status in health and disease.
Serum Ionized Magnesium
The use of magnesium-specific, ion-selective electrodes to more accurately assess extracellular free magnesium levels is a promising new technology. This technique correlates well with intracellular free magnesium levels in conditions such as diabetes, chronic renal failure and pregnancy.
Intracellular free magnesium
Nuclear magnetic resonance (NMR) spectroscopy is the most definitive and noninvasive measure of the active magnesium ion in blood cells or tissues. The lack of routine availability of NMR has limited its clinical use so far.
Sublingual magnesium assay
The 'EXA Test' is a safe, non-invasive test that accurately measures the minerals inside cells. This is a test used, for example, during cardiac surgery to determine cellular magnesium levels. A doctor painlessly collects a sample from under your tongue and affixes it to a slide. The slide is then sent to IntraCellular Diagnostics, Inc. for analysis.
Magnesium Loading Test
This test measures urinary magnesium excretion in response to a loading dose of magnesium. Although inconvenient to perform, this test has successfully identified individuals with even mild degrees of magnesium deficiency. It has been considered the most accurate test when renal function is normal.
Hypomagnesemia (<1.7meq/L) is found in 7% of routine screenings, but is far more prevalent in patients with diabetes (20% to 50%) and in patients in the intensive care unit (20% to 65%).
There is a possibility that magnesium deficiency contributes to pulmonary complications. The authors note during the past few years there has been an increase in calcium consumption in the U.S. but little change in magnesium intake, which may imbalance the calcium:magnesium ratio. Serum levels can be normal and yet there can be magnesium deficiency within cells. These authors believe pulmonary patients should be routinely monitored for magnesium deficiency. There have been noted benefits of magnesium for wheezing also.[Role of Magnesium in Regulation of Lung Function, The Journal of the American Dietetic Association, June 1993;93(6): pp.674-677]
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