Test library
Magnesium Deficiency Test
The Magnesium Blood Test measures magnesium in serum or plasma to help evaluate deficiency or excess. Magnesium is involved in muscle and nerve function, heart rhythm, energy metabolism, and bone health.
Order Magnesium Levels Blood Test
Order online and visit a local collection site, or choose an at-home kit where available. No referral and no insurance required.
Order Magnesium Levels Blood Test- Typical turnaround
- 1-3 business days
- Starting price
- From $28
- Results
- Confidential, online
Quick answer
The Magnesium Blood Test measures the amount of magnesium in the liquid portion of the blood. Magnesium is a mineral the body uses in hundreds of processes, including muscle contraction, nerve signaling, heart rhythm, blood pressure regulation, and bone structure. The test is ordered when low or high magnesium is suspected, when a condition or medicine can affect magnesium balance, or as part of a broader metabolic evaluation.
What this test measures
Magnesium is found mainly inside cells and in bone, with only a small fraction circulating in the blood. A serum magnesium measurement is the most common way to assess status, but it captures that circulating fraction rather than total body stores. Even so, an abnormal serum level is a meaningful finding that guides further evaluation.
The sample is a standard blood draw. Because about a third of circulating magnesium is bound to albumin, a low albumin level can make total serum magnesium look lower than the active fraction; some laboratories measure or estimate albumin to help with interpretation. Ionized magnesium, the unbound form, can also be measured when a more precise view is needed.
The test may be ordered when a person has muscle cramps, weakness, irregular heartbeat, or digestive symptoms, or when conditions such as kidney disease, diabetes, or alcohol use may disturb magnesium balance. Certain medicines, including some diuretics and acid-reducing drugs, can also affect levels. A qualified healthcare provider interprets the result with the person's history and other laboratory findings.
- Magnesium (serum or plasma)
- Albumin
- Calcium
- Potassium
- Creatinine
- Estimated glomerular filtration rate (eGFR)
- Ionized magnesium when included
- Blood urea nitrogen (BUN) when included
Why people order this test
- Evaluate symptoms that may relate to low or high magnesium
- Check magnesium when kidney function is impaired
- Monitor magnesium when a medicine can affect levels
- Follow up on an abnormal magnesium value from another panel
- Assess magnesium as part of a metabolic evaluation
How to prepare
No fasting is usually required for a magnesium blood test, but follow the laboratory's instructions. Tell the collection staff about any medications or supplements you take, because some can influence the result.
Understanding your results
Results are typically available within one to three business days. A value below or above the reference range can reflect changes in intake, absorption, kidney handling, or other factors. A qualified healthcare provider determines what the result means in context.
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Frequently Asked Questions
What is magnesium and why does it matter?
Magnesium is a mineral involved in muscle and nerve function, heart rhythm, energy production, and bone health. The test shows how much is circulating in the blood.
Does a normal serum magnesium rule out deficiency?
Not always. Because most magnesium is stored inside cells and in bone, serum levels can appear normal even when body stores are low. A provider may order additional testing.
What can cause low magnesium?
Possible causes include poor intake, digestive losses, kidney losses, diabetes, alcohol use, and some medicines. A qualified healthcare provider identifies the likely reason.
Is fasting needed for this test?
Fasting is usually not required for magnesium alone, but follow the instructions on the laboratory order for your appointment.
Can supplements affect the result?
Yes. Magnesium supplements and some medicines can change blood levels, so tell the collection staff what you take so the result can be interpreted accurately.
Ready to get tested?
Order online and visit a collection site near you, or choose a mail-in kit. No referral and no insurance required.
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