Synonyms: Mg

Why It Is Done

Determine a cause for nerve and muscle problems, such as muscle twitches, irritability, and muscle weakness.
Determine the cause of a low calcium or potassium level that is not improving despite treatment.
Screen for an excess of magnesium or for a magnesium deficiency (especially in people taking diuretics).
Determine whether people with heart problems need additional magnesium. Low magnesium levels can increase the risk of potentially life-threatening heart rhythm problems.
Measure levels when magnesium is being given for medical treatment.

Test Overview

A magnesium test measures the level of magnesium in the blood. Magnesium is an important electrolyte needed for proper muscle, nerve, and enzyme function. It also helps regulate energy production in cells and is needed to move other electrolytes (potassium and sodium) into and out of cells.

Magnesium is one of the most abundant minerals in the body and is found mainly inside the bones and cells. Only a tiny amount of magnesium is normally present in the blood. It is absorbed through the small intestine during food digestion. A balanced diet contains enough magnesium for the body's needs.

How To Prepare

Do not take medications containing magnesium for at least 3 days before this test. This includes antacids that contain magnesium, certain laxatives (such as milk of magnesia or Epsom salts), magnesium supplements, and certain diuretics.