Serum or plasma concentration of magnesium
This test measures the amount of magnesium, a mineral essential for many bodily functions, in your blood.
["Magnesium helps with muscle and nerve function and keeps your bones strong."]
Key facts at a glance
- LOINC
- 31912-9
- Short code
- N men Ag Spec Ql
- Synonyms
- N men Ag Spec Ql
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What Is Magnesium Used For in the Body?
Magnesium plays a key role in over 300 chemical reactions in your body, including helping muscles and nerves work properly, maintaining healthy bones, and supporting energy production. Low levels can affect how your body uses other nutrients, while high levels may cause health concerns that need monitoring.
Why Might You Need This Test?
Your doctor may order a magnesium test to check for deficiencies or excesses, especially if you have symptoms like muscle weakness, cramps, irregular heartbeat, or conditions like kidney disease, diabetes, or certain medications that affect magnesium levels.
What to Expect Before the Test
You may need to fast for a few hours before the test, depending on the lab instructions. Bring any medications you’re currently taking, as some can affect results. Avoid drinking alcohol or taking magnesium supplements 24 hours before the test.
What Happens During the Test?
A healthcare provider will draw blood from a vein in your arm. You may feel a small pinch, but it usually doesn’t cause discomfort. The blood sample is sent to a lab for analysis.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Magnesium Level
Frequently asked questions
Low magnesium levels can lead to muscle spasms, numbness, high blood pressure, or even heart rhythm problems. High levels may cause nausea, weakness, or irregular heartbeat and can sometimes be dangerous if untreated. Your doctor will interpret results in the context of your overall health.
Results are typically available within 1 to 3 business days, depending on your lab. Your doctor will contact you once they have the full report.
Follow your lab’s instructions, but generally, you should avoid food for a few hours before the test and avoid alcohol or magnesium supplements for 24 hours before drawing blood.
Sources
- 1
- 2Lab Tests OnlineSource
- 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 16, 2026. · Read our editorial policy