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Magnesium (Blood)

Does this test have other names?


What is this test?

This test measures the amount of the mineral magnesium in your blood. Magnesium is found in your cells and bones. It's necessary for many different chemical reactions in your body. Your heart needs magnesium to beat properly. Your muscles need magnesium to contract and relax. Your nerves need magnesium to send signals. Magnesium also plays a role in controlling blood sugar and blood pressure. Your body uses magnesium to absorb calcium.

Why do I need this test?

You may have this test if you have signs and symptoms that might be caused by too much or too little magnesium. These can include:

  • Weakness

  • Muscle cramps

  • Numbness or tingling

  • Irregular heartbeat

  • Nausea

  • Diarrhea

  • Confusion or slurred speech

  • Seizures

You may also have this test if you have kidney problems, diabetes, alcoholism, or some other conditions, or if other blood tests show you have abnormal levels of other minerals, such as calcium, potassium, or phosphorus.

If you are pregnant, your doctor may watch your magnesium levels to make sure you don't develop preeclampsia, a serious complication marked by protein in your urine and high blood pressure.

What other tests might I have along with this test?

You may have other blood tests to measure levels of other minerals or substances in your blood. You may also have a test to check for magnesium in your urine.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Results are given in milliequivalents per liter (mEq/L). Normal test results are:

  • 1.3 to 2.1 mEq/L for adults

  • 1.4 to 1.7 mEq/L for children

  • 1.4 to 2 mEq/L for newborns

Abnormal magnesium levels may have many possible causes. For example, increased levels of magnesium may be seen with kidney disease because magnesium is excreted by the kidneys. A low magnesium level can be a sign of diabetes, some digestive problems, malnourishment, or alcoholism. Lower magnesium levels during pregnancy may mean preeclampsia.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Some drugs, such as antacids and laxatives, can cause magnesium levels to rise. Other drugs, such as some antibiotics, insulin, and diuretics, can cause magnesium levels to drop.

How do I get ready for this test?

You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.