Risks

Blood test

There is very little risk of complications from having blood drawn from a vein.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Normal

Many conditions can change magnesium levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.

What Affects the Test

High values

High magnesium levels may be caused by:

• Dehydration.
• Diseases of the adrenal glands, such as Addison's disease.
• An overactive parathyroid gland (hyperparathyroidism).
• An underactive thyroid gland (hypothyroidism).
• Kidney failure.
• The use of medicine that contains magnesium, such as antacids and laxatives.

Low values

Low magnesium levels may be caused by:

• Alcohol abuse or withdrawal.
• Complications from diabetes, such as diabetic ketoacidosis.
• Diseases that block with the way food is absorbed in the intestines, such as sprue.
• High blood calcium levels (hypercalcemia).
• Infection and swelling of the pancreas (pancreatitis).
• Kidney disease.
• Long-term diarrhea.
• Not getting enough magnesium in the foods you eat.
• Pregnancy, especially in the second or third trimester.
• Underactive parathyroid glands (hypoparathyroidism).

What To Think About

• A test for magnesium may be done along with testing for other electrolytes, such as calcium, chloride, potassium, and phosphorus. For more information, see the topics Calcium (Ca) in Blood, Chloride (Cl), Potassium (K) in Blood, and Phosphate in Blood.
• The amounts of magnesium and calcium in the body are closely related.
• Having low magnesium levels is rare. Symptoms of a magnesium deficiency include weakness, dizziness, irregular heartbeat, shaking, twitching, and seizures. Low magnesium levels are usually caused by not eating enough of the foods that contain magnesium or from problems that block the way food is absorbed from the intestines.