Magnesium (Mg)
Test Overview A magnesium test checks the level of
magnesium in the blood. Magnesium is an important
electrolyte needed for proper muscle, nerve, and
enzyme function. It also helps the body use
energy and is needed to move other electrolytes (potassium and sodium) into and
out of cells. Most of the magnesium in the body is found in the
bones and inside the cells. Only a tiny amount of magnesium is normally present
in the blood. Tests for other electrolytes, such as calcium,
potassium, sodium, and phosphorus, may be done along with a test for
magnesium. Why It Is DoneA test for magnesium is done to: - Find a cause for nerve and muscle problems,
such as muscle twitches, irritability, and muscle weakness.
- Find
the cause of symptoms such as low blood pressure, nausea, vomiting, diarrhea,
dizziness, muscle weakness, and slurred speech.
- Monitor kidney function.
- Find the cause of
heart problems or trouble breathing, especially in people who have kidney
disease.
- Find the cause of a low calcium or potassium level that is
not improving with treatment.
- Look for changes in magnesium levels
caused by medicines, such as
diuretics.
- See if people who have heart
problems need extra magnesium. Low magnesium levels can increase the chances of
life-threatening heart rhythm problems.
- Measure levels when
magnesium is being given for medical treatment.
How To PrepareMany medicines may change the results
of this test. Be sure to tell your doctor about all the nonprescription and
prescription medicines you take. Do not take medicines containing magnesium
for at least 3 days before this test. This includes antacids that contain
magnesium, laxatives (such as milk of magnesia or Epsom salts), magnesium
supplements, and some
diuretics. Talk to your doctor about any
concerns you have regarding the need for the test, its risks, how it will be
done, or what the results will mean. To help you understand the importance of
this test, fill out the
medical test information form(What is a PDF document?). How It Is DoneThe health professional drawing blood
will: - Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
alcohol.
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
blood.
- Remove the band from your arm when enough blood is
collected.
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure on the site and then put on a
bandage.
How It FeelsThe blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch. RisksBlood testThere 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.
ResultsThe 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. NormalMany 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 TestHigh valuesHigh magnesium levels may be caused
by: Low valuesLow 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.
- 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.
ReferencesCitations- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Other Works Consulted- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
CreditsByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Adam Husney, MD - Family Medicine
Martin J. Gabica, MD - Family Medicine
Specialist Medical ReviewerMartin J. Gabica, MD - Family Medicine Current as ofOctober 14, 2016 Current as of:
October 14, 2016 Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins. Last modified on: 8 September 2017
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