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Serum magnesium - test

A serum magnesium test is a measurement of how much magnesium there is in the blood.

Alternative Names

Magnesium - blood

How the test is performed

Blood is most often drawn from a vein. The vein usually used is on the inside of the elbow or the back of the hand.

The procedure is done in the following way:

  • The site is cleaned with germ-killing medicine (antiseptic).
  • The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
  • A needle is gently inserted into the vein.
  • The blood collects into an airtight vial or tube attached to the needle.
  • The elastic band is removed.
  • The needle is removed.
  • The puncture site is covered with an adhesive strip to stop any bleeding.

For infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. Afterward, a bandage may be placed over the area if there is any bleeding.

How to prepare for the test

No special preparation is needed.

How the test will feel

When the needle is inserted to draw blood, you may feel slight pain, or a prick or stinging. Afterward, there may be some throbbing.

Why the test is performed

This test is done when your health care provider suspects you may have an abnormal level of magnesium in your blood.

About half of the body's magnesium is found in bone. The other half is found inside cells of body tissues and organs.

Magnesium is needed for nearly all chemical processes in the body. It helps maintain normal muscle and nerve function, and keeps the bones strong. Magnesium is also needed for the heart to function normally and to help regulate blood pressure. Magnesium also helps the body control blood sugar level and helps support the body's defense (immune) system.

Normal Values

1.7 to 2.2 mg/dL

Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.

What abnormal results mean

A high magnesium level may indicate:

A low magnesium level may indicate:

What the risks are

There is very little risk in having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks may include:

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

References

Klemm KM, Klein MJ. Biochemical markers of bone metabolism. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 15.

Mason JB. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 225.

Updated: 1/22/2013

Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.


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