Magnesium Blood Test

A magnesium blood test measures the amount of magnesium in a sample of your blood. Magnesium is a mineral that you get from many kinds of foods you eat. Some examples include nuts, seeds, beans, fortified breakfast cereals, green leafy vegetables, and milk.

Your body needs magnesium to help your muscles, nerves, and heart work properly. Magnesium also helps control blood pressure and blood glucose, also called blood sugar. It's important for building strong bones, and it supports your immune system.

Magnesium is a type of electrolyte. Electrolytes are electrically charged minerals. They help control the amount of fluid and the balance of acids and bases (pH balance) in your body.

Most of your body's magnesium is stored in your bones, organs, and other body tissue. Only a small amount is found in your blood. Your body tightly controls the amount of magnesium in your blood mainly through your: Kidneys.

They filter extra magnesium from your blood and get rid of it through urine (pee). If your magnesium level is low, your kidneys limit the amount lost through urine.; Intestines. They control how much magnesium you absorb from the foods you eat.; Abnormal levels of blood magnesium can be caused by many different conditions.

So, a magnesium test may be used to help diagnose a variety of disorders.

Why this test is done

You may need a magnesium blood test if you have symptoms that could be caused by abnormal magnesium levels.

Symptoms of low magnesium include:

• Loss of appetite
• Nausea and vomiting
• Fatigue and weakness
• Muscle cramps
• Numbness and/or tingling
• Irregular heartbeat (arrhythmia)
• Seizures (if magnesium levels are extremely low)

Symptoms of high magnesium are much the same as symptoms of low magnesium. They may also include:

• Diarrhea
• Abdominal (belly) cramping
• Cardiac arrest from extremely high levels of magnesium

You may also need to have your magnesium levels checked to monitor your health if you:

• Have a condition that's linked to abnormal magnesium levels, such as:
• Chronic kidney disease
• Diabetes that's not well controlled
• Alcohol use disorder
• Malabsorption syndrome
• Malnutrition
• Chronic (long-lasting) diarrhea
• Low levels of potassium and/or calcium
• Take medicine that can decrease magnesium levels, for example:
• Diuretics ("water pills")
• Certain antibiotics
• Proton pump inhibitors to reduce stomach acid
• Take medicine that can increase magnesium levels, for example:
• Aspirin
• Medicines that contain magnesium, such as laxatives for constipation and certain antacids for heartburn or gastroesophageal reflux disease (GERD)
• Lithium
• Are being treated with magnesium and/or calcium.

How to prepare

There's usually no preparation for a magnesium blood test. If you're having other blood tests at the same time, you may need to fast (not eat or drink) for several hours before your test.

Your provider will let you know if you need to prepare for your test. Be sure to tell your provider about any prescription and over-the-counter medicines and/or supplements that you are taking.

Sample type

Blood

Other names for this test

Mg, Mag, Magnesium-Serum