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Magnesium, Serum or Plasma Concentration

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of magnesium, a mineral essential for many bodily functions, in your blood. It helps assess whether your levels are too high or too low, which can affect muscle, nerve, and heart health.

Quick summary

["Magnesium levels help identify potential deficiencies or excesses that may require medical attention."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
19123-9
Short code
Magnesium SerPl-mCnc
Synonyms
Magnesium SerPl-mCnc
Category
electrolyte
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
1.7
Ref high
2.2
Critical range
1 N/A – 5 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
83735
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

Why Is This Test Done?

Doctors may order a magnesium test to diagnose conditions like low magnesium (hypomagnesemia), which can cause muscle weakness, irregular heartbeat, or seizures. It may also be checked if you have symptoms like nausea, vomiting, or tremors. Additionally, it can help monitor magnesium levels in people with kidney disease, heart conditions, or certain medications that affect magnesium absorption.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it involves a blood draw. If you’re taking magnesium supplements or certain medications, inform your healthcare provider beforehand. Avoid strenuous activity or caffeine for a few hours before testing.

What Happens During the Test?

A healthcare professional will draw blood from a vein in your arm. The blood sample is then sent to a lab for analysis. The test typically takes a few minutes, and you may feel slight discomfort but no lasting effects.

What Are Possible Results?

Results are reported as a numerical value representing the magnesium concentration in your blood (usually in milligrams per deciliter, mg/dL). While reference ranges vary by lab, low or high levels may signal underlying health concerns that need further evaluation.

Reference range

Adult: 1.7-2.2 mg/dLN/A

Specimen: serum

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: When Low or High Magnesium Levels Matter

Short name

Magnesium Level

Frequently asked questions

What Are Common Causes of Low Magnesium?
Low magnesium (hypomagnesemia) can result from poor diet (low intake of foods like nuts, leafy greens, or whole grains), certain medications (e.g., diuretics, some antibiotics), chronic kidney disease, or malabsorption issues (e.g., celiac disease). It may also occur in people with excessive vomiting, diarrhea, or heavy sweating.
What Are Common Causes of High Magnesium?
High magnesium (hypermagnesiumemia) is less common but can occur in kidney failure (since kidneys normally regulate magnesium), excessive magnesium supplements or laxatives, or certain medical conditions like adrenal insufficiency. Rarely, it may appear in people with severe dehydration or overuse of antacids containing magnesium.
How Does This Test Relate to My Overall Health?
This test helps doctors diagnose and manage conditions affecting magnesium balance, such as muscle spasms, irregular heart rhythms, or neurological symptoms. Regular monitoring may be needed if you have chronic health conditions like diabetes, heart disease, or kidney problems that influence magnesium levels.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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