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Serum or plasma concentration of magnesium (qualitative or semi-quantitative screening)

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

This test measures the level of magnesium in your blood, either as a general check or to identify if your levels are too high or too low.

Quick summary

["Magnesium helps your muscles and nerves work properly, and low levels can cause weakness or cramps."]

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

Key facts at a glance

LOINC
65763-5
Short code
N men Ag Tiss Ql ImStn
Synonyms
N men Ag Tiss Ql ImStn
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
immune-stain
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 Done

Your doctor may order this test if you have symptoms like muscle spasms, weakness, irregular heartbeat, or if you have conditions like kidney disease, diabetes, or certain medications that affect magnesium levels. It can also be part of routine monitoring for people with chronic health issues.

What to Expect Before the Test

You may need to fast for a few hours before the test, depending on your doctor’s instructions. Bring any medications you’re currently taking, as some can affect magnesium levels. Avoid drinking alcohol before the test.

What Happens During the Test

A healthcare provider will draw blood from a vein in your arm. You might feel a small pinch, but it usually doesn’t cause discomfort. The blood sample is then sent to a lab for analysis.

What the Results Mean

Results are qualitative (yes/no) or semi-quantitative (approximate ranges), meaning they help determine if levels are abnormal rather than providing exact numbers. Your doctor will interpret the results in the context of your health and symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Frequently asked questions

What could cause abnormal magnesium levels?
Low magnesium (hypomagnesemia) can be caused by poor diet, kidney problems, vomiting, diarrhea, or certain medications. High magnesium (hypermagnesemia) is less common but can occur with kidney failure, overuse of magnesium supplements, or certain medical conditions.
How might my doctor use these results?
Your doctor may use these results to adjust treatments, such as dietary changes, medications, or further testing if needed. They’ll also consider your overall health and symptoms to guide next steps.
Do I need to prepare differently if I’m pregnant or have a specific condition?
Yes, if you’re pregnant, have kidney disease, or take medications like diuretics or antibiotics, your doctor may give you specific instructions. Always follow their guidance to ensure accurate 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