Magnesium
A serum magnesium test measures the amount of magnesium in your blood, an essential mineral that supports muscle function, nerve function, and energy production.
{"Magnesium is a vital mineral that helps your muscles, nerves, and heart work properly","Low magnesium levels (hypomagnesemia) can cause muscle cramps, fatigue, and irregular heartbeats","High magnesium levels (hypermagnesemia) are less common but can be serious","The test uses a small blood sample taken from a vein in your arm","Normal range is typically 1.7 to 2.2 mg/dL, but reference ranges may vary"}
Key facts at a glance
- LOINC
- 19123-9
- Short code
- MAG
- Synonyms
- —
- Category
- electrolyte
- Sample
- serum
- Container
- Serum Separator Tube (SST/Gold Top) or Plain Red Top Tube
- Units
- mg/dL
- Ref low
- 1.7
- Ref high
- 2.2
- Critical range
- 1 mg/dL – 4.5 mg/dL
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- methylthymol-blue
- CPT
- 83735
- SNOMED
- 365906006
- Specimen volume
- 3-5 mL
- Stability
- Room temperature: 7 days, Refrigerated (2-8°C): 7 days, Frozen (-20°C or below): 30 days
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 1–4 hours
What is a Magnesium Test?
A magnesium blood test, also called a serum magnesium test, measures the concentration of magnesium in your blood. Magnesium is an essential electrolyte and mineral that plays a crucial role in many bodily functions, including muscle contraction, nerve signaling, blood pressure regulation, and protein synthesis.
Why Do I Need This Test?
Your doctor may order a magnesium test if you have symptoms of abnormal magnesium levels, such as muscle twitches or cramps, fatigue, weakness, irregular heartbeat, or numbness. It may also be ordered if you have conditions that affect magnesium absorption, such as kidney disease, diabetes, or gastrointestinal disorders, or if you are taking medications that can affect magnesium levels.
How Is the Test Performed?
A healthcare professional will draw a small amount of blood from a vein in your arm using a needle. The blood sample is then sent to a laboratory for analysis. The test is quick and typically takes only a few minutes. You may experience slight discomfort or bruising at the puncture site, but serious complications are rare.
Understanding Your Results
Normal serum magnesium levels typically range from 1.7 to 2.2 mg/dL (0.85 to 1.10 mmol/L). However, reference ranges may vary slightly depending on the laboratory. Low magnesium (hypomagnesemia) may indicate poor dietary intake, malabsorption, certain medications, or chronic conditions. High magnesium (hypermagnesemia) is less common and often relates to kidney dysfunction or excessive magnesium supplementation.
Preparing for the Test
No special preparation is usually required for a magnesium blood test. However, inform your doctor about all medications and supplements you are taking, as some can affect test results. Fasting is not typically required, but follow any specific instructions provided by your healthcare provider.
Reference range
Adult reference range: 1.5-2.5 mg/dL. Pediatric ranges may vary by age. Therapeutic range for patients on magnesium supplementation: 1.7-3.0 mg/dL.mg/dL
No fasting required. Patient should inform laboratory of current medications including magnesium supplements, diuretics, and proton pump inhibitors. Avoid intravenous fluids containing magnesium for 4 hours prior to collection when possible.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Mg
Part of panels
Frequently asked questions
What are the symptoms of low magnesium?
What causes low magnesium levels?
How is low magnesium treated?
Can I take magnesium supplements before the test?
Is fasting required for a magnesium blood test?
Sources
- 1
- 2
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 10, 2026. · Read our editorial policy