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 magnesium.
Why It Is Done
A test for magnesium is done to:
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 diuretics.
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 will:
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 pinch.
There is very little risk of complications from having blood drawn from a vein.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Many conditions can change magnesium levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.
What Affects the Test
High magnesium levels may be caused by:
Low magnesium levels may be caused by:
What To Think About
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