Magnesium Blood Test: Purpose, Preparation, and Results

A magnesium blood test measures the amount of magnesium, an important mineral, in your blood. Your body needs magnesium from your diet to help your muscles, nerves, heart, and immune system work properly. Magnesium also helps control blood pressure and blood sugar and build strong bones.

Your kidneys, bones, intestines, and hormones regulate the amount of magnesium in your blood. However, many conditions can change your magnesium blood level. Detecting high or low magnesium levels in your blood can help your healthcare provider diagnose certain diseases and disorders.

Your healthcare provider may order a magnesium blood test to check if the magnesium levels in your blood are too low or high. You might be asked to get a magnesium blood test for the following reasons:

To Investigate Symptoms

If you have low magnesium, also known as magnesium deficiency or hypomagnesemia, your symptoms may include:

• Loss of appetite
• Nausea
• Vomiting
• Muscle cramps
• Numbness or tingling
• Fatigue
• Weakness
• Irregular heartbeat (arrhythmia)
• Seizures

If your magnesium is high, also known as hypermagnesemia, you may have the same symptoms of low magnesium as well as the following:

• Diarrhea
• Abdominal cramping
• Cardiac arrest (when the heart suddenly stops beating)

To Monitor Effects of a Condition

Your healthcare provider may also use this test to help monitor your health if you have a condition associated with abnormal magnesium levels. These can include:

• Alcohol use disorder
• Chronic kidney disease
• Chronic diarrhea
• Diabetes
• Malnutrition from an eating disorder or other cause
• Low levels of potassium or calcium

To Monitor Effects of a Medication

If you take certain medications that can affect your magnesium levels, your healthcare provider may order a magnesium blood test to monitor your levels. These medications include:

• Antibiotics
• Aspirin
• Diuretics
• Laxatives
• Lithium
• Proton pump inhibitors
• Magnesium or calcium supplements

To Determine Why Other Mineral Levels Are Abnormal

Magnesium plays a critical role in maintaining the balance and proper functioning of other minerals in the body, such as calcium, potassium, and phosphorus. It helps regulate processes like calcium metabolism and potassium transport across cell membranes.

If your levels of these other minerals are abnormal, your healthcare provider may order a magnesium blood test to see if your magnesium levels are playing a role.

You usually don’t need to prepare for a magnesium blood test in any special way.

This test is sometimes done with other blood tests that require fasting, so you may need to avoid eating and drinking for a specified time in those cases. Your healthcare provider can let you know if you need to fast.

Let your healthcare provider know of any supplements and medications you’re taking. They may tell you to change your regimen leading up to the test.

Your healthcare provider will take a sample of blood from a vein in your arm. That sample gets sent to a lab for analysis.

To take the sample, your provider will tightly tie a band around your arm to temporarily stop blood flow, making it easier for them to find a vein. They’ll sterilize the site where they plan to insert the needle, usually with rubbing alcohol. Then, they’ll insert a small needle into your vein and draw the blood into a tube or vial.

You’ll need to stay still as your blood is being drawn. You may feel a slight sting when the needle is inserted and removed. After removing the needle, your healthcare provider will tell you to apply pressure on the site where the needle was inserted before they place a bandage over the site. The whole test typically takes under five minutes.

After giving your blood sample for the test, you can return to normal activities. You may feel some discomfort from where the needle was inserted, but it should go away shortly.

There is little risk to a magnesium blood test. Just like any blood test, you might experience slight discomfort or bruising where the needle was inserted.

Some people might feel faint when they get blood drawn. If you’ve ever fainted during a blood test, tell the person drawing your blood beforehand. They may have you lie down as a precaution.

Your results should be available in a few days. Your healthcare provider will contact you with your results or send them through a patient portal.

Interpreting Your Results

A normal magnesium blood level is typically between 0.75-0.95 millimoles.

Different factors can affect your magnesium levels. For low or high magnesium levels, your healthcare provider will consider these levels along with your medical history and other tests to make a diagnosis.

Low Magnesium Levels

Low magnesium generally means you’re not getting enough magnesium from food, or your body can’t absorb the mineral even if you are getting enough. Low magnesium may be caused by conditions like:

• Alcohol use disorder: Trouble with stopping or controlling alcohol use
• Chronic diarrhea: Loose or watery stools that occur three or more times per day for four weeks or longer
• Hyperaldosteronism: When the adrenal glands produce too much of the hormone aldosterone
• Malnutrition: When the body doesn’t get enough nutrients to function properly
• Pancreatitis: Inflammation of the pancreas
• Ulcerative colitis: A condition that causes inflammation in the lining of the colon and rectum
• Uncontrolled diabetes: Complications from high blood sugar, leading to damage of your kidneys and the nervous and cardiovascular systems

High Magnesium Levels

Higher magnesium levels could mean you’re getting too much of the mineral from medications (like laxatives and antacids), supplements, and food. It’s rare to take in too much magnesium from food alone.

Another cause of high magnesium is a medical condition that interferes with your body’s ability to regulate your magnesium level. Conditions that can lead to high magnesium levels include:

• Kidney failure: The most common condition to cause high magnesium because magnesium is mostly regulated by your kidneys
• Adrenal insufficiency: The adrenal glands do not produce enough hormones
• Dehydration: A loss of too much fluid from your body, which can affect kidney function and reduce how much magnesium is removed from the body

A magnesium blood test reveals the level of magnesium in your blood. Magnesium is a mineral involved in many vital functions, and your kidneys and hormones are primarily responsible for maintaining a healthy level of magnesium in your body.

If a magnesium blood test indicates your levels are too high or low, it could be a sign of a health condition that needs treatment—possibly relating to your kidneys or hormones.