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Total Serum/Plasma Magnesium Concentration

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

This test measures the amount of magnesium in your blood serum or plasma, an important mineral for muscle and nerve function, blood clotting, and bone health.

Quick summary

["Magnesium levels help assess risks for muscle cramps, heart rhythm issues, or electrolyte imbalances."]

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

Key facts at a glance

LOINC
518-1
Short code
TMP SMX Titr SBT
Synonyms
TMP SMX Titr SBT
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
sbt
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?

Your doctor may order this test to check for low magnesium (hypomagnesemia) if you have symptoms like muscle spasms, irregular heartbeat, or seizures. It may also be done to monitor conditions like kidney disease, alcohol use, or certain medications that affect magnesium levels.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for a few hours before the blood draw if your test is part of a metabolic panel. Bring any medications you’re currently taking.

What Happens During the Test?

A healthcare provider will draw blood from a vein in your arm. You may feel a slight pinch, but the process is quick. The blood sample is sent to a lab for analysis.

What the Results Mean

Results are compared to standard reference ranges for healthy adults. Low levels may indicate health concerns, while high levels could signal kidney disease or other conditions. Your doctor will interpret results in the context of your overall health.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Total Serum Magnesium

Frequently asked questions

What causes low magnesium levels?
Low magnesium can result from poor diet (low intake of foods like nuts, leafy greens, or whole grains), certain medications (e.g., diuretics, antibiotics), kidney disease, or excessive vomiting/diarrhea.
What causes high magnesium levels?
High magnesium is less common but can occur with kidney failure (where the body can’t remove excess magnesium), overuse of magnesium supplements, or certain medications (e.g., laxatives).
Do I need to avoid certain foods before the test?
No specific foods are restricted, but if your test is part of a metabolic panel, your doctor may advise fasting. Magnesium-rich foods (like spinach or almonds) won’t affect the test results.
  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