Alternative names
Serum magnesium - test

Definition
This is a test that measures the amount of magnesium in the blood.

How the test is performed

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 airtight 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

There is no special preparation for this 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:

 
• Infant test or procedure preparation (birth to 1 year)  
• Toddler test or procedure preparation (1 to 3 years)  
• Preschooler test or procedure preparation (3 to 6 years)  
• School age test or procedure preparation (6 to 12 years)  
• Adolescent test or procedure preparation (12 to 18 years)

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 found 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 (the major source of energy for all cells).

Normal Values

1.8 to 3.0 mg/dL

What abnormal results mean

High magnesium levels may be seen with the following conditions:

 
• Addison’s disease  
• Chronic renal failure  
• Dehydration  
• Diabetic ketoacidosis  
• Oliguria

Low magnesium levels may be seen with the following conditions:

 
• Alcoholism  
• Chronic diarrhea  
• Delirium tremens  
• Administration of excessive insulin  
• Hemodialysis  
• Hepatic (liver) Cirrhosis  
• Hyperaldosteronism  
• Hypoparathyroidism  
• Pancreatitis  
• Toxemia of pregnancy  
• Ulcerative colitis

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

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.

Medical Encyclopedia

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.