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The Blood Test for Magnesium

written by: A. Jitesh•edited by: Emma Lloyd•updated: 7/6/2010

The blood test for magnesium is performed when the doctor suspects an alteration in the levels of this mineral in the body. Why the test is ordered, how the test is performed, the normal levels of magnesium in the blood and how to interpret blood magnesium test report is described in this article.

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    Magnesium (Mg) is a mineral that in a healthy human being, is found mostly in bones and inside cells. Magnesium is usually found in its ionic form (Mg2+) and is hence an electrolyte, like sodium and potassium. Its function is to aid in transfer of these ions in and out of cells, thereby helping in proper function of nerve cells, muscle cells and certain enzymes.

    The blood test for magnesium is a test used to measure the level of magnesium in a blood sample. It is often a part of the electolyte panel, but can also be independently prescribed.

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    Why is it Ordered

    There are multiple reasons a doctor may order the blood test for magnesium:

    1. Muscular weakness or twitching
    2. Cardiac arrhythmia
    3. Low blood pressure coupled with muscle weakness and dizziness.
    4. To check the effects of medications known to alter levels of magnesium in the body.
    5. To check the effects of therapy for high or low magnesium levels.
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    How is it done

    Before the test is performed, one must ensure that the patient has not consumed antacids, laxatives, milk of magnesia, Epsom salts or other magnesium supplements for three days prior to the test. Blood is withdrawn in a vacutainer or tube and sent to the laboratory for the test. Less than 5 mL is sufficient for this test, and results are usually available in 24 hrs.

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    What the Levels Mean

    Normal levels in adults are between 1.6 to 2.6 mg/dL. Children have a normal range of 1.7 - 2.1 mg/dL while in infants and newborn babies, it is 1.5-2.2 mg/dL.

    A level less than 1 mg/dL is said to be critical and indicative of Hypomagnesemia - <1 mg/dL, whereas critical hypermagnesia is when the levels exceed 5 mg/dL.

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    How Diagosis is Performed

    Conditions indicative of low Mg

    • Hypoparathyoidism
    • Hyperthyroidism
    • Mg deficiency
    • diabetic ketoacidosis
    • pancreatic inflammation
    • alcolhol abuse or alcohol withdrawal symptoms
    • Pre-eclampsia
    • ulcerative colitis

    Conditions indicative of high Mg

    • Consumption of medication (antacids/laxatives) having magnesium
    • Hyperparathyroidism
    • Hypothyroidism
    • Addison's Disease
    • Dehydration
    • Renal failure

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    Other Tests for Mg

    More than 55% of the magnesium in our body is present in the bones, with another 26% in the muscles and 18% in various tissues. That leaves only 1% free in circulation in blood. It follows that the blood test for magnesium is not one the best tests to diagnose deficiency of this mineral in our bodies.There are other tests available to measure the total magnesium levels in our body, but these tests are not readily available in most hospitals, and are tedious to carry out, requiring much specialized, extremely expensive equipment.

    1. NMR test - very tedious, requires tissue samples of patient, requires specialized equipment, very expensive, not readily available, very accurate

    2. Mg Load Test - tedious, requiring regular urine sample collection over extended time periods. Not suitable unless hospitalized.

    Consult a registered medical practitioner as he would be the best person to prescribe an appropriate test for your requirements.

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    References and Further Reading

    1. Delmar's Guide to Laboratory and Diagnostic Tests By Rick Daniels
    2. The Magnesium Factor By Mildred S. Seelig, Andrea Rosanoff
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