1. Standard serum blood test (most used, least reliable):
Experts agree that serum magnesium blood tests fail to identify deficiency because less than 1% of magnesium is in our serum, and our body tightly regulates our serum magnesium to stay within the “healthy range” that this test checks.
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.) There are two problems with this test:
- 99% of magnesium is in our cells and less than 1% is in our blood serum.
- 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.  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.
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.”
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.”
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.
2. Exatest (most accurate, least accessible):
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:
- 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.
- Most insurance companies to not cover this test, and without insurance it is expensive, priced at many hundreds of dollars.
- 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.
3. Ionized test (most accurate, least accessible):
Professors Bella and Burton Altura developed this test in the 1990’s at the State University of New York  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.
4. RBC test (highly accurate, more accessible):
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:
- It is more widely recognized and covered by health insurance.
- Even when not covered by insurance, the RBC test is much more affordable.
- 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 and Dynacare. While some research also now points towards using magnesium levels in immune cells as good indicators, the RBC test is currently the best option based on the combined factors of reliability, availability, and price.
5. Magnesium loading test (relatively accurate, not practical):
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 deficient 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.