Magnesium
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- Also Known As:
- Mg
- Mag

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At a Glance
When To Get Tested?
When you have symptoms such as weakness, irritability, cardiac arrhythmia, nausea, and/or diarrhea that may be due to too much or too little magnesium; when you have abnormal calcium or potassium levels; when magnesium is given for medical treatment
Sample Required?
A blood sample drawn from a vein in your arm; sometimes a timed urine collection that most often requires a 24-hour sample collection
Test Preparation Needed?
For a blood sample, overnight fasting may be required; follow any instructions that you are given.
You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Testing.com. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.
Testing.com is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.
The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.
If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.
Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.
While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”
For more information, please read the article Reference Ranges and What They Mean.
What is being tested?
Magnesium is a mineral that is vital for energy production, muscle contraction, nerve function, and the maintenance of strong bones. It comes into the body through the diet and is absorbed by the small intestine and colon. Magnesium is stored in the bones, cells, and tissues. Normally, only about 1% of total body magnesium is present in the blood and this makes it difficult to get an accurate measurement of total magnesium content from blood tests alone. However, this test is still useful for evaluating a person’s magnesium status.
A wide variety of foods contain small amounts of magnesium, especially green vegetables such as spinach, as well as whole grains and nuts. Foods that have dietary fiber are usually also sources of magnesium. The body maintains its magnesium level by regulating how much it absorbs and how much it excretes or conserves in the kidneys.
Magnesium deficiencies (hypomagnesemia) may be seen with malnutrition, conditions that cause malabsorption, and with excess loss of magnesium by the kidneys. Magnesium excess (hypermagnesemia) may be seen with the ingestion of antacids that contain magnesium and with decreased ability of the kidneys to excrete magnesium.
Someone with mild to moderate magnesium deficiency may have no or few nonspecific symptoms. Persistent or severe deficiencies can cause nausea, loss of appetite, fatigue, confusion, muscle cramps, seizures, changes in heart rate, and numbness or tingling. They can also affect calcium metabolism and exacerbate calcium deficiencies. Symptoms of excess magnesium can be similar to those of deficiency and include nausea, muscle weakness, loss of appetite, and an irregular heart rate.
Common Questions
View Sources
Sources Used in Current Review
2017 review performed by Jagadish K. Boppisetti, PhD, Senior Scientist.
(Updated: February 11, 2016) Magnesium Fact Sheet for Health Professionals. Office of Dietary Supplements (ODS), National Institutes of Health. Available online at https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/. Accessed June 2017.
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; 2012:159-175.
Guerra M, et al. Therapeutic Uses of Magnesium. Am Fam Physician. 2009 Jul 15;80(2):157-162. Available online at http://www.aafp.org/afp/2009/0715/p157.html. Accessed on 06/29/2017.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
NIH (2001 August 7, Updated). Magnesium. NIH Clinical Center, National Institutes of Health, Facts About Dietary Supplements [On-line information]. Available online at http://www.cc.nih.gov/ccc/supplements/magn.html.
Rude, R. [Reviewed] (2001 February 05, Updated). Magnesium. Linus Pauling Institute [On-line information]. Available online at http://www.orst.edu/dept/lpi/infocenter/minerals/magnesium/.
Zangwill, M. [Updated] (2001 February 01, Updated). Magnesium in diet. MedlinePlus Health Information [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/002423.htm.
Angelo, S. [Updated] (2001 November 05, Updated). Serum magnesium test. MedlinePlus Health Information [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003487.htm.
Merck. Magnesium Metabolism. The Merck Manual of Diagnosis and Therapy [On-line information]. Available online at http://www.merck.com/pubs/mmanual/section2/chapter12/12f.htm.
Spengler, R. (2001 June 25, Updated). Magnesium (Mg). WebMDHealth [On-line information]. Available online at http://my.webmd.com/encyclopedia/article/4118.278.
(Updated 2009 July 13). Magnesium. NIH, Office of Dietary Supplements [On-line information]. Available online at http://ods.od.nih.gov/factsheets/magnesium.asp. Accessed March 2010.
Vorvick, L. (Updated 2009 March 9). Magnesium in Diet. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/002423.htm. Accessed March 2010.
(2005 January). U.S. Department of Health and Human Services and U.S. Department of Agriculture. Dietary Guidelines for Americans, 2005. 6th Edition, Washington, DC: U.S. Government Printing Office. Chapter 2 Adequate Nutrients Within Calorie Needs [On-line information]. Available online at http://www.health.gov/dietaryguidelines/. Accessed March 2010.
Novello, N. and Blumstein, H. (Updated 2009 August 18). Hypomagnesemia. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/767546-overview. Accessed March 2010.
Ferry, R. (Updated 2010 January 8). Hypermagnesemia. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/921382-overview. Accessed March 2010.
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 640-641.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 706-709.
Magnesium, 24 Hour, Urine. Mayo Clinic. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/8595. Accessed October 2013.
Elin, R.J. Assessment of magnesium status for diagnosis and therapy. National Center for Biotechnology Information PubMed Database. Available online at http://www.ncbi.nlm.nih.gov/pubmed/20736141?dopt=Abstract. Accessed October 2013.
Dietary Supplement Fact Sheet: Magnesium. National Institutes of Health, Office of Dietary Supplements. Available online at http://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/. Accessed October 2013.
Serum magnesium. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003487.htm. Accessed December 2013.
Magnesium measurement, urine. MUSC Health. Available online at http://www.muschealth.com/lab/content.aspx?id=150515. Accessed December 2013.
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