Magnesium

What is magnesium?

Magnesium is an essential mineral involved in the work of more than three hundred enzymes in the body. It plays a role in many functions, such as energy production, muscle contraction and relaxation, nerve transmission, regulation of heart rhythm, maintenance of bone structure and blood sugar balance. Green leafy vegetables, nuts, whole grains and legumes are good sources of magnesium. Magnesium from food is absorbed in the intestines, and the excess is excreted in the urine via the kidneys.

Most of the body's magnesium is found in the bones and inside cells; the amount circulating in the blood is less than one percent of total stores. So even when the blood level is normal, there may be a mild deficiency in the body's stores. Because some of the magnesium in the blood is carried bound to proteins, the albumin level may also be taken into account when interpreting the result. The test is run on the serum portion of blood drawn from the arm using colorimetric methods and is usually evaluated together with other minerals such as calcium and potassium.

When is a magnesium test ordered?

Because magnesium imbalances often cause vague symptoms, the test is ordered when the cause of symptoms is being investigated or when there is a condition that may disturb magnesium balance. Magnesium deficiency is also looked for particularly when low potassium and low calcium levels are hard to correct, because these minerals affect one another. In people with kidney disease, regular measurement may be needed because magnesium can build up in the blood. If magnesium treatment has been started, your doctor may also repeat the test to see the effect of the treatment.

• Muscle cramps, twitching, tremor or muscle weakness
• Unexplained palpitations and signs of an abnormal heart rhythm
• Prolonged diarrhea, malabsorption disorders or heavy alcohol use
• Use of diuretics or long-term use of stomach acid-suppressing medications
• Uncontrolled diabetes and low potassium or calcium that is hard to correct
• Kidney disease or use of medications and supplements containing magnesium

How do I prepare for a magnesium test?

You usually do not need to fast for a magnesium measurement; however, if your doctor has also ordered tests that require fasting, such as blood sugar or cholesterol, at the same time, you will need to give blood in the morning before breakfast. Magnesium supplements, magnesium-containing stomach medications and laxatives can raise the blood level. If you use these products, ask your doctor whether you should pause them before the test, and do not stop your prescribed medications on your own.

Diuretics, some antibiotics and long-term use of stomach-protecting medications, on the other hand, can lower magnesium levels; it is therefore important that you report all the medications you take. When blood is drawn from an arm vein, care is taken to prevent hemolysis, the breakdown of red blood cells, because magnesium leaking from red blood cells can make the result falsely high. If you wish, a nurse can take this sample at your home or at your workplace.

What does a magnesium result mean?

Low magnesium, or hypomagnesemia, can develop due to inadequate nutrition, prolonged diarrhea, intestinal absorption problems, heavy alcohol use, uncontrolled diabetes and certain medications. It can cause symptoms such as muscle cramps, weakness, tremor and palpitations, and often occurs together with low potassium and low calcium. Mild deficiencies may cause no symptoms at all and may be picked up incidentally on routine tests. When a deficiency is found, the treatment plan is set by your doctor according to the underlying cause.

High magnesium, by contrast, is rarer and mostly occurs when the kidneys cannot excrete magnesium adequately or when magnesium-containing medications and supplements are overused. A marked elevation can cause nausea, weakness, low blood pressure and reduced reflexes. The normal limits for magnesium can differ slightly from laboratory to laboratory, as well as with age and sex; the range of the laboratory that analyzes your test is shown on this page. It is your doctor who will interpret your result together with other findings, such as calcium, potassium and kidney tests, and with your symptoms.