If my magnesium level is low, what steps can I take to correct it?

Start by increasing dietary magnesium through foods like leafy greens, nuts, seeds, and whole grains. If needed, your clinician may prescribe a magnesium supplement and investigate underlying causes such as chronic diarrhea, kidney dysfunction, or certain medications.

Should I stop taking magnesium supplements before the test, and how will supplements affect the results?

Yes, it is best to discontinue magnesium supplements 24–48 hours before the blood draw, as they can artificially raise serum levels and mask an underlying deficiency.

What symptoms might lead my doctor to order a magnesium blood test?

If you experience unexplained muscle cramps, twitches, fatigue, irregular heartbeats, or low blood pressure, your doctor may check magnesium levels to rule out a deficiency that can affect muscle and nerve function.

How long does it take to receive my magnesium test results, and what do the normal ranges look like?

Results are usually available within 1–3 business days. Normal serum magnesium is about 1.7–2.2 mg/dL (0.7–0.9 mmol/L); values below or above this range may indicate hypomagnesemia or hypermagnesemia.

Magnesium Blood Test

A magnesium blood test measures the levels of this essential mineral in your blood to help diagnose various health conditions and monitor electrolyte balance.

What is a magnesium blood test?

A magnesium blood test measures the amount of magnesium in a sample of your blood. Magnesium is a mineral obtained from foods such as nuts, seeds, beans, fortified breakfast cereals, green leafy vegetables, and milk.

Your body requires magnesium for proper muscle, nerve, and heart function. It also helps control blood pressure and blood glucose (blood sugar), supports the immune system, and is essential for building strong bones.

Magnesium is an electrolyte—an electrically charged mineral that helps control fluid levels and the body's pH balance. While most of your body's magnesium is stored in bones and organs, a small amount circulates in the blood. Levels are tightly controlled by the:

Kidneys: They filter excess magnesium and excrete it through urine, or limit loss if levels are low.
Intestines: They regulate how much magnesium is absorbed from food.

Other names: Mg, Mag, Magnesium-Serum

What is it used for?

This test checks for abnormal magnesium levels, which may indicate underlying health issues. It is also used to investigate abnormal levels of other minerals, such as calcium, potassium, and phosphorus, because magnesium influences how the body absorbs them.

Low magnesium (hypomagnesemia): A magnesium deficiency; this is more common than high levels.
High magnesium (hypermagnesemia): An uncommon condition, most often occurring in people with kidney failure.

Why do I need a magnesium blood test?

You may need this test if you exhibit symptoms of abnormal magnesium levels or have a condition that affects these levels.

Symptoms of Low Magnesium

Loss of appetite
Nausea and vomiting
Fatigue and weakness
Muscle cramps
Numbness and/or tingling
Irregular heartbeat (arrhythmia)
Seizures (in extreme cases)

Symptoms of High Magnesium

Diarrhea
Abdominal cramping
Cardiac arrest (in extreme cases)

Monitoring may also be required if you have chronic kidney disease, poorly controlled diabetes, alcohol use disorder, malabsorption syndrome, malnutrition, or chronic diarrhea. Additionally, certain medications—including diuretics, antibiotics, proton pump inhibitors, aspirin, laxatives, and lithium—can affect magnesium levels.

What happens during a magnesium blood test?

A health care professional will take a blood sample from a vein in your arm using a small needle. The process typically takes less than five minutes.

Will I need to do anything to prepare for the test?

There is usually no preparation required. However, if you are having other blood tests simultaneously, you may need to fast for several hours. Inform your provider about all prescription and over-the-counter medicines and supplements you are taking.

Are there any risks to the test?

There is very little risk. You may experience slight pain or bruising at the needle site, which typically resolves quickly.

What do the results mean?

Your provider will interpret results based on your medical history and other test findings.

Low magnesium levels may indicate:

Insufficient dietary intake.
Malabsorption issues, such as Crohn's disease.
Excessive loss of magnesium due to kidney problems, long-term diarrhea, or diabetes.

High magnesium levels may indicate:

Excessive intake from supplements, laxatives, or antacids.
Inability of the body to excrete magnesium, most commonly due to kidney failure.

Is there anything else I need to know?

Blood levels may appear normal even if total body stores are low, as the body pulls magnesium from bones to maintain blood stability. Providers may order a magnesium urine test or a magnesium red blood cell (RBC) test for a more comprehensive assessment.