Magnesium Testing Information

You have asked Dr. Dean about magnesium testing. Here are two relevant sections from her 2017 Edition of The Magnesium Miracle:




You’ve heard the saying “To err is human, to forgive is di­vine”? In the medical world, to err is human, to test is di­vine. I’m not a huge fan of laboratory tests because the results are compared to average values in our unhealthy popula­tion, not to optimal values. And errors can occur. I tell my readers that lab testing should be used to confirm what our senses and intuition tells us. But all too often doctors place all their faith in tests and only glance at the results, looking for numbers above or below normal.


When it comes to supplementing with magnesium, I do not think that the majority of people require testing. Magne­sium is extremely safe, and it does produce a laxative effect when you take too much at one time or when you are satu­rated with magnesium after several months of supplementa­tion. Even with ReMag, which is fully absorbed at the cellular level, when cell saturation is reached you will experi­ence the laxative effect. I encourage you to follow your mag­nesium deficiency symptoms and the “100 Factors Related to Magnesium Deficiency,” in Chapter 1 [of the Magnesium Miracle], as guides to how much magnesium you should take. (Or read the blog “Gauging Magnesium Deficiency”)





The magnesium RBC test is more accurate than the serum magnesium test, but it’s not as accurate as the ionized mag­nesium test, which is only available in research labs. Since it’s not highly accurate, please don’t just let the numbers be the gauge of how you are doing; you must also keep track of your magnesium deficiency symptoms and assess whether they are improving as you treat yourself with magnesium.


Your doctor or your local lab may not even know about the magnesium RBC test. Don’t worry; the test can be ob­tained easily online if your doctor can’t or won’t write you a requisition for it. Go to or and type in “magnesium RBC.” You will be asked for your zip code and sent to a local lab for a blood draw. You will receive your results within seventy-two hours. The test only costs about $49, which may be less than the copay for an office visit so your doctor can write you a lab order. (Note: This type of testing is not available in all states.)


Be aware that lab values for magnesium don’t give you an optimum or a therapeutic range. The lab just measures the magnesium level of people that walk in the door and charts them on a bell curve. The current magnesium range for most labs is 4.2–6.8 mg/dL, but recently I’ve seen some labs go even lower, to 3.5–6.0 mg/dL, as the population gets more and more deficient! About 80 percent of the population is deficient in magnesium, so I tell people that for optimal health, we want to be at the high end of the range, at or above the 80th percentile, or about 6.0–6.5 mg/dL.


You can repeat the test every three to six months and use it as a guide for the form of magnesium you should take and how much. However, you may find that the second test after three months produces a result that is the same as the first test or even lower, yet you are feeling better. That’s because the 700–800 enzyme systems that require magnesium are getting all revved up and using more and more magnesium, so the levels can dip down in the beginning of treatment. Then at the six-and nine-month stages, your levels will be higher as you become more saturated. It can take a year or more for you to reach full saturation and begin to need less magnesium. Read “How Much Magnesium Should I Take?” in the Introduction and “What Magnesium Should I Take?” in Chapter 18 for more guidance.


A huge caveat in lab testing is that doctors only look at “red-flagged” results, those that are out of range, so if they do your magnesium RBC test and the result is 3.8 mg/dL, you will be told that your magnesium is normal. But you’re really at the bottom rung of magnesium and probably expe­riencing many magnesium deficiency symptoms. If you want to pull yourself out of that heap and eliminate your symp­toms, you want to take enough magnesium to reach a level of 6.0–6.5 mg/dL.


Another reason the magnesium RBC test is still not the perfect test is because there are no mitochondria in red blood cells. There are mitochondria in all the cells of the body ex­cept red blood cells. Each liver cell has between 1,000 and 2,000 mitochondria, for example. Mitochondria are the en­ergy factories inside cells. Six of the eight steps to make ATP (the energy molecule) in the mitochondrial Krebs cycle re­quire magnesium. Therefore, there will be a lot more mag­nesium in cells that contain mitochondria than in red blood cells. The superior test is the ionized magnesium test, which does not measure the magnesium in cells but measures the ionized magnesium in the blood, which is the type of mag­nesium that is readily absorbed into the cell. But this test is not available outside of research settings.


Below are the normal ranges for magnesium RBC test­ing using the three different measurements that are com­monly used worldwide. If your test results come back in mmol/L, multiply that result by 2.433 to give you the result in mg/dL. Remember that you want your magnesium RBC levels to be optimal, about 6.0–6.5 mg/dL. You want to be above the 80th percentile of the population, as 80 percent of people are deficient in magnesium.


Magnesium Test           mg/dL              mmol/L            mEq/L

Mg RBC                       4.2–6.8            2.4–2.57          3.37–5.77

Note: Do not take magnesium for at least 12 hours before your test.



In the first 3-6 months the RBC levels can actually go down as the body sweeps up all the ReMag to activate the 700-800 enzyme processes. What you follow is how you feel.