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Magnesium, Serum or Plasma Mass Concentration

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

This test measures the amount of magnesium in your blood (either serum or plasma). Magnesium is an essential mineral that helps with muscle and nerve function, blood pressure regulation, and bone health.

Quick summary

["Your magnesium level helps doctors check for deficiencies or excesses that could affect your health."]

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

Key facts at a glance

LOINC
20872-8
Short code
Magnesium Ocflu-mCnc
Synonyms
Magnesium Ocflu-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 This Test Might Be Ordered

Doctors may order a magnesium test if you have symptoms like muscle weakness, cramps, irregular heartbeat, or signs of low magnesium (such as nausea, vomiting, or seizures). It may also be done to monitor conditions like kidney disease, heart problems, 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 doctor specifies. Bring any medications or supplements you take, as they can influence results.

What the Test Results Mean

Results are compared to standard reference ranges, but exact values can vary by lab. Low magnesium levels may indicate deficiencies, while very high levels could signal medical conditions or side effects from certain treatments.

Common Conditions Linked to Magnesium Levels

Low magnesium (hypomagnesemia) can cause muscle spasms, irregular heart rhythms, or weakness. High magnesium (hypermagnesia) is less common but may occur in kidney failure or overuse of magnesium supplements.

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.

◆Associated findings1

Short name

Magnesium Level

Frequently asked questions

What causes magnesium levels to be checked?
Magnesium tests are often done if you have symptoms like muscle cramps, irregular heartbeat, or unexplained fatigue. They may also be part of routine checks for conditions like kidney disease, diabetes, or heart problems.
How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab. Your doctor will contact you once they have the full report.
Can I take magnesium supplements before the test?
If your doctor prescribed magnesium supplements, follow their instructions. Avoid large doses unless directed, as they can affect test accuracy. Always check with your healthcare provider before taking supplements.
  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