Magnesium Deficiency Testing

Learn why standard magnesium blood tests are dangerously misleading. See which tests are more reliable, and how to find out if you’re deficient without paying for tests.

++ Page Overview

Why test? To prevent disease. When tests show we have low magnesium, we then know we need to restore it with diet and supplements. The longer our organs are deficient in magnesium the more damage we suffer. This guide looks at all available magnesium tests:

  1. Standard serum blood test: least reliable.
  2. Exatest: very reliable but not practical.
  3. Ionized blood test: most reliable, not accessible.
  4. RBC test: reliable and most accessible/affordable.
  5. Loading/tolerance test: requires multiple hospital visits
  6. Simple, logical self-test.

We begin by learning why the standard tests that medical doctors use are incapable of accurately identifying magnesium deficiency:

++ Helpful tip
This page has a lot of powerful info to help you resolve your problems. 

If you’re busy or want to understand things better, please read each section’s quick summary.

1. Serum blood tests are unreliable:


The standard method of testing magnesium levels is the serum blood test (the healthy range is 1.5 to 2.4 mg/dl or 0.7 – 1 mmol/L.)[1] There are two problems with this test:

1. 99% of magnesium is in our cells and less than 1% is in our blood serum.

2. Our blood serum does NOT paint an accurate picture of the magnesium levels in our cells because our body takes magnesium from our cells and organs to keep our blood serum levels within the desired healthy range. [2] This is because magnesium in our blood also plays a vital role in electrolyte balance, which can result in sudden death if disturbed enough.[3-5]

Simply put, standard blood tests check magnesium levels in a place where our body keeps our magnesium levels within a relatively stable range. Blood serum may in fact be the worst indicator for magnesium levels and thus identifying deficiency.


Experts agree:

The magnesium in our blood serum does not accurately reflect whether the rest of our organs and tissues are deficient. Dr. Ronald Elin of the Department of Pathology and Laboratory Medicine at the University of Louisville agrees stating:

“Serum and red blood cell magnesium concentrations have been shown to be poor predictors of intracellular magnesium concentration.”[6]

Professor Judy Driskell from the department of Nutrition and Health Sciences at the University of Nebraska further confirms the evasive nature of magnesium deficiency:

“Normal serum and plasma magnesium concentrations have been found in individuals with low magnesium in [red blood cells] and tissues. Yet efforts to find an indicator of subclinical magnesium status have not yet yielded a cost-effective one that has been well validated.”[7]

The effectiveness of blood tests to spot magnesium deficiency has also been studied by doctors Dierck-Harmut and Dierck-Ekkehard Liebscher who have concluded in the Journal of the American College of Nutrition that a staggering 50% of magnesium deficiencies may be going untreated as a result of the unreliability of serum testing.[8]

++ Summary
Experts agree that serum magnesium blood tests often fail to identify deficiency because:

Less than 0.5% of magnesium is in our serum, and our body tightly regulates our serum magnesium to stay within the “healthy range” that the test checks.

2. More Reliable Testing Methods:

++ Exatest: sublingual test

The intracellular test offered by Exatest is far superior to the serum blood test done by most doctors. It uses a scraper to take a sample of the sub-lingual epithelial cells in our mouth’s lining. Instead of measuring blood serum, this test measures magnesium in our cells. Although very accurate, there are several downfalls to using the Exatest:

  1. This test is not easily accessible as there is only one laboratory in the world that processes Exatest samples into results, in Medford Oregon, USA.
  2. Most insurance companies to not cover this test, and without insurance it is expensive,  priced at many hundreds of dollars.
  3. There is a degree of skill required by the health professional to take a sample of the subject’s sublingual cells. Unlike taking a blood sample, this process is vulnerable to human error.

While the Exatest does provide more accurate results when samples are taken properly, for most of us it is not very practical.

++ Ionized magnesium test:

Professors Bella and Burton Altura developed this test in the 1990’s at the State University of New York [9] where it is currently being run. Instead of our serum, this test measures human blood. More specifically it uses advanced technology to measure the actual magnesium ions in our blood. This is powerful because the magnesium ion (lone positively charged magnesium atom) is what is so critical to most of our vital processes.

While this test is very accurate, and the procedure is simpler than the Exatest, it is also barely accessible due to the few locations that offer it.

++ RBC test: the easiest option

This test is also more accurate than the serum test because it also measures the magnesium in our cells instead of our serum. More specifically, it measures magnesium in our red blood cells (RBC), which have been shown to reflect the levels of magnesium in our other cell types accurately.[10,11] The RBC test has several benefits over the Exatest:

  1. It is more widely recognized and covered by health insurance.
  2. Even when not covered by insurance, the RBC test is much more affordable.
  3. There is no added training the health professional needs to take your sample, which makes the measuring and test results more reliable.

Various organizations and clinics in North America offer the RBC test for between $40 to $105 including: Request-a-test, Dynacare, and While some research also now points towards using magnesium levels in immune cells as good indicators,[12] the RBC test is currently the best option based on the combined factors of reliability, availability, and price.

++ Magnesium loading (tolerance) test

The magnesium loading test works in the opposite direction as the other tests. Here doctors inject magnesium into the blood of patients, and measure the amount that is excreted via the urine, for up to 48 hours later.[13,14]

The idea is that the less magnesium we excrete, the more our body needs and thus the more deficienct we are. Experts are divided on the reliability of this test[15,16]: There may be other factors in the body that may impact the excretion of magnesium, which have nothing to do with deficiency.

Furthermore the test requires at least one visit back to the doctor’s office within 24 hours of injection, which makes it less economical.

++ Summary
The Exatest and Ionized test are both extremely reliable but not practical, easily accesible nor affordable for most people.

The Magnesium Red Blood Cell test (RBC) is also far more accurate than the serum test, and is more affordable and readily available than the above two.

3. No resources? Do your own test:

If you’re not in the position to get an RBC or Exatest, simple logic can help you see if you’re deficient. You simply need to connect these facts:

  1. Every organ, muscle and nerve uses magnesium everyday, and this never changes.
  2. All stress depletes magnesium, and our environmental stress is increasing everyday.
  3. Our only sources of magnesium – our food and water – are now depleted.

Because of all our magnesium-dependent bodily processes, we need a specific amount of magnesium everyday. If we ingest less than that amount daily, then we are developing a deficiency with every passing day and experts now agree it is very difficult to get enough magnesium without supplementation.



Most doctors use the serum blood test which rarely spots magnesium deficiency. The Exatest, Ionized test and RBC tests provide reliable results, and the RBC is the most practical.

Whether we choose to perform tests or not, it is wise to make dietary and lifestyle changes that favour healthy magnesium levels.

Click here to see the best (and tricky) magnesium-rich foods.

Click here for a simple guide on the different molecular forms of magnesium supplements.

Click here to see why magnesium chloride is a good base for a magnesium restoration program.

++ References
  1. Medscape: Magnesium Serum Blood test Reference Range.
  2. Magnesium metabolism. A review with special reference to the relationship between intracellular content and serum levels.
  3. The other electrolytes: magnesium, calcium, and phosphorus.
  4. Heart failure and electrolyte disturbances.
  5. Significance of magnesium in congestive heart failure.
  6. Calcium and magnesium in drinking-water: Public health significance.
  7. Nutrition and exercise concerns of middle age.
  8. About the Misdiagnosis of Magnesium Deficiency.
  9. Blood Ionized Magnesium Test: Drs. Bella and Burton Altura. State University of New York, Health Science Center at Brooklyn, New York, New York 11203, USA. (718) 270-2194 or (718) 270-2205.
  10. Erythrocyte intracellular Mg(2+) concentration as an index of recognition and memory.
  11. Assessment of magnesium status in newly diagnosed diabetic children: measurement of erythrocyte magnesium level and magnesium tolerance testing.
  12. A New In Vitro Blood Load Test Using a Magnesium Stable Isotope for Assessment of Magnesium Status.
  13. Magnesium deficiency diagnosed by an intravenous loading test.
  14. The magnesium loading test: reference values in healthy subjects.
  15. Rude RK. Magnesium. In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Baltimore, Mass: Lippincott Williams & Wilkins; 2012:159-75.
  16. Volpe SL. Magnesium. In: Erdman JW, Macdonald IA, Zeisel SH, eds. Present Knowledge in Nutrition. 10th ed. Ames, Iowa; John Wiley & Sons, 2012:459-74. 2017 Ι This website is designed by the artists at  Contact us at