| Definition: |
This is a test that measures the amount of magnesium in the blood.
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| Alternative Names: |
Mg+2; Serum Magnesium
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| How the test is performed: |
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and cause veins below the tourniquet to distend with blood. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding. |
| How to prepare for the test: |
Fast for 4 hours before the test.
Infants and children:
The physical and psychological preparation involved in readying a child for any test or procedure depends on the child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| How the test will feel: |
| When the needle is inserted to draw blood, some people may feel moderate pain, while others may feel only a prick or stinging sensation. Afterward, there may be some throbbing. |
| Why the test is performed: |
This test is performed when an abnormal blood level of magnesium is suspected.
About half of the body's magnesium is present in bone, where it plays a structural role (along with calcium, phosphate, and various proteins). In all other tissues magnesium is among the most abundant of all the intracellular (inside the cell) electrolytes, second only to potassium. Magnesium is necessary for essentially all biochemical processes. For example, synthesis and use of ATP (ATP is the major source of energy for all cells). |
| Normal Values: |
1.8 to 3.0 mg/dl
Note: mg/dl = milligrams per deciliter |
| What abnormal results mean: |
| Greater-than-normal magnesium levels may be seen in:Lower-than-normal magnesium levels may occur in:
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| What the risks are: |
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
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| Special considerations: |
| Veins and arteries vary in size from one patient to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. |
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