A serum magnesium test measures the level of magnesium in the blood.
How the Test is Performed
A blood sample is needed.
How the Test will Feel
When the needle is inserted to draw blood, some people feel slight pain. Others feel a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
How to Prepare for the Test
No special preparation is needed.
The normal range for blood magnesium level is 1.7 to 2.2 mg/dL (0.85 to 1.10 mmol/L).
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
There is very little risk in having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
What Abnormal Results Mean
A high magnesium level may indicate:
- The adrenal glands are not producing enough hormones (Addison disease)
- Loss of kidney function (chronic renal failure)
- Loss of body fluids (dehydration)
- Diabetic ketoacidosis, a life-threatening problem in people with diabetes
- Producing less urine than usual (oliguria)
A low magnesium level may indicate:
- Alcoholism or severe alcohol withdrawal (delirium tremens)
- Long-term (chronic) diarrhea
- Treatment to remove waste from the blood (hemodialysis)
- Scarring of the liver and loss of liver function (cirrhosis)
- Adrenal gland produces too much of the hormone aldosterone (hyperaldosteronism)
- Parathyroid glands do not produce enough parathyroid hormone (hypoparathyroidism)
- Inflammation of the pancreas (pancreatitis)
- Too much insulin
- High blood pressure and protein in the urine in a pregnant woman (preeclampsia)
- Inflammation of the lining of the large intestine and rectum (ulcerative colitis)
Why the Test is Performed
This test is done when your health care provider suspects you have an abnormal level of magnesium in your blood.
About half of the body's magnesium is found in bone. The other half is found inside cells of body tissues and organs.
Magnesium is needed for many chemical processes in the body. It helps maintain normal muscle and nerve function, and keeps the bones strong. Magnesium is also needed for the heart to function normally and to help regulate blood pressure. Magnesium also helps the body control blood sugar level and helps support the body's defense (immune) system.
Chernecky CC, Berger BJ. Magnesium— serum. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:750-751.
Klemm KM, Klein MJ. Biochemical markers of bone metabolism. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. St Louis, MO: Elsevier; 2017:chap 15.
Mason JB. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 218.