Magnesium (Blood)

Mg

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 correctly. 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.

You may need this test if you have 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 healthcare provider may watch your magnesium levels to make sure you don't develop preeclampsia. This is a serious complication marked by protein in your urine and high blood pressure.

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.

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

Results are given in milligrams per deciliter (mg/dL). Normal test results are generally in the range of:

• 1.8 to 2.6 mg/dL for adults

• 1.7 to 2.1 mg/dL for children

• 1.5 to 2.2 mg/dL 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 long-term (chronic) alcoholism. Lower magnesium levels during pregnancy may mean preeclampsia.

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore. 

Some medicines, such as antacids and laxatives, can cause magnesium levels to rise. Medicines, such as some antibiotics, insulin, and water pills (diuretics), can cause magnesium levels to drop.

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