A magnesium test checks the level of
magnesium in the blood. Magnesium is an important
electrolyte needed for proper muscle, nerve, and
enzyme function. It also helps the body use
energy and is needed to move other electrolytes (potassium and sodium) into and
out of cells.
Most of the magnesium in the body is found in the
bones and inside the cells. Only a tiny amount of magnesium is normally present
in the blood.
Tests for other electrolytes, such as calcium,
potassium, sodium, and phosphorus, may be done along with a test for
Why It Is Done
A test for magnesium is done to:
- Find a cause for nerve and muscle problems,
such as muscle twitches, irritability, and muscle weakness.
the cause of symptoms such as low blood pressure, nausea, vomiting, diarrhea,
dizziness, muscle weakness, and slurred speech.
- Monitor kidney function.
- Find the cause of
heart problems or trouble breathing, especially in people who have kidney
- Find the cause of a low calcium or potassium level that is
not improving with treatment.
- Look for changes in magnesium levels
caused by medicines, such as
- See if people who have heart
problems need extra magnesium. Low magnesium levels can increase the chances of
life-threatening heart rhythm problems.
- Measure levels when
magnesium is being given for medical treatment.
How To Prepare
Many medicines may change the results
of this test. Be sure to tell your doctor about all the nonprescription and
prescription medicines you take. Do not take medicines containing magnesium
for at least 3 days before this test. This includes antacids that contain
magnesium, laxatives (such as milk of magnesia or Epsom salts), magnesium
supplements, and some
Talk to your doctor about any
concerns you have regarding the need for the test, its risks, how it will be
done, or what the results will mean. To help you understand the importance of
this test, fill out the
medical test information form(What is a PDF document?).
How It Is Done
The health professional drawing blood
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure on the site and then put on a
How It Feels
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or