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Blood Test Tracker

Magnesium

Magnesium is a mineral your muscles, nerves and heart need. A blood test shows only a small part of your body's total supply.

AI-verified against cited sources. Awaiting expert reviewAlso called MgLOINC 19123-9

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What it is

Magnesium helps more than 300 chemical reactions in your body. It supports nerve and muscle function, keeps your heartbeat steady and helps keep bones strong. You get it from food such as leafy greens, nuts, beans and whole grains. Only about 1% of your body's magnesium is in your blood and the fluid around your cells, and about half is stored in bone, so a blood test is a small snapshot.

Why it matters

Low magnesium often shows up together with low potassium and low calcium. It can cause muscle cramps, tremor, weakness or an uneven heartbeat. Very high levels are uncommon and mostly happen when the kidneys can't remove magnesium. Because blood holds so little of the body's magnesium, a result inside the range does not always rule out low stores, and a low result is worth reading with your potassium, calcium and kidney tests.

If it’s low

A low result means there is less magnesium in your blood than usual. Mild lows often cause no symptoms. A lower level can cause tiredness, nausea, weakness, muscle cramps, tremor or an irregular heartbeat, often along with low potassium or calcium. Many causes are common, such as long-term diarrhea or certain medicines, and your clinician can sort out which one fits.

Common causes

  • Long-term diarrhea, or bowel conditions or surgery that reduce absorption
  • Water pills (loop and thiazide diuretics)
  • Long-term use (over a year) of acid-reducing medicines called proton pump inhibitors
  • Heavy alcohol use
  • Poorly controlled diabetes
  • Some other medicines, such as certain antibiotics (aminoglycosides, amphotericin B), cisplatin and cyclosporine
  • Absorbing less magnesium, which is more common in older adults and people with type 2 diabetes

What can help

  • Ask your clinician whether a medicine, diarrhea or alcohol use could explain it
  • Ask whether potassium, calcium and kidney function should be checked too
  • Eat magnesium-rich foods such as dark leafy greens, nuts, seeds, beans and whole grains
  • Talk with your clinician before taking magnesium supplements, especially if you have kidney disease

If it’s high

A high magnesium result is uncommon. It usually means the kidneys are not clearing magnesium well, or that someone is taking a lot of magnesium-containing laxatives or antacids. It can also come from a blood sample with damaged red cells. Mild increases often cause no symptoms. Your clinician can put your result in context.

Common causes

  • A sample problem, such as damaged red cells in the tube (hemolysis)
  • Reduced kidney function, the most common true cause
  • Magnesium-containing laxatives or antacids, especially when kidney function is low
  • Magnesium sulfate given in hospital, for example during pregnancy for preeclampsia
  • Dehydration
  • An underactive thyroid, overactive parathyroid glands or Addison disease

What can help

  • Tell your clinician about every antacid, laxative and supplement you use
  • Ask whether the test should be repeated or whether your kidney function should be checked

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on age. Choose an age to see the one that applies.

Children and teens 5 ranges

See Magnesium by age and sex, with the U.S. survey numbers where they exist.

Wellness targets

Narrower ranges some clinicians aim for. Being outside one doesn’t mean something is wrong.

2.1–2.3 mg/dL (18+). Evidence: Limited. A 2022 review by magnesium researchers (MaGNet) recommends 0.85 mmol/L (2.07 mg/dL) as the lower limit, because lower levels have been linked to higher risk of heart and metabolic disease, and it cites 0.85–0.95 mmol/L (2.07–2.3 mg/dL) as a range another group suggested. Only 2 of the 43 lab ranges the authors collected used this cutoff, and they say an upper limit still has to be set.

How common is your level?

NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.

How Magnesium varies with age in the U.S.Shaded: middle 90% and middle 50% of people. Line: the median. mg/dL. Point at any age, or focus the chart and use the arrow keys, to read both sexes in words.

Use the left and right arrow keys to read each age. Shift moves five years.

Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.

Explore Magnesium by age and sex: every percentile as a table, with a download.

What can affect your result

  • Sample handling: red cells hold two to three times more magnesium than serum, so damaged cells raise the result
  • High bilirubin may make some methods read falsely low
  • Kidney function, which controls how much magnesium you keep
  • Diarrhea, alcohol use, diabetes and medicines such as water pills and acid reducers
  • Age: children's upper limits are a little higher than adults'
  • Lab differences: the lower limit is 1.6 mg/dL at Labcorp and 1.7 mg/dL at Mayo Clinic Laboratories, and some researchers propose 2.07 mg/dL
  • Red blood cells hold two to three times more magnesium than serum, so a sample with damaged red cells (hemolysis) can read falsely high. Mayo Clinic Laboratories rejects grossly hemolyzed samples.
  • High bilirubin may make some methods read falsely low (Labcorp).
  • EDTA and citrate plasma are not acceptable samples (Labcorp). Serum or plasma should be separated from the cells promptly: Labcorp asks for within 45 minutes and Mayo Clinic Laboratories within 2 hours.
  • Magnesium-containing antacids, laxatives and supplements, and magnesium given by IV in hospital, can raise the level. Tell your clinician about everything you take.

Hours to days for the blood level, for example after diarrhea, a medicine change or IV magnesium. Because only about 1% of body magnesium is outside the cells, it may not reflect slower changes in total stores.

When to talk to a clinician

Contact the clinician who ordered the test soon if your result is outside your lab's range, especially with muscle cramps, tremor, weakness, palpitations or unusual drowsiness, or if you have kidney disease and use magnesium-containing laxatives or antacids. ARUP treats results below 1.0 or above 9.0 mg/dL as urgent. Call 911 or your local emergency number for chest pain, a seizure, fainting, very slow or shallow breathing, or extreme drowsiness.

Questions you could ask

  • Does my magnesium level matter for any of my other conditions or medicines?
  • How often should it be checked?
  • Could my kidney function, or an antacid, laxative or supplement I take, explain a higher result?
  • Should we repeat the test?
  • Could a medicine, my diet, digestion or alcohol use explain a lower result?
  • Should we check my potassium, calcium and kidney function too?

Questions people ask

Does a normal magnesium result mean my body has enough?

Not always. Only about 1% of your body's magnesium is in your blood and the fluid around your cells, and the body keeps that level steady by drawing on bone and cells. So the level can look fine even when stores are lower. If you have symptoms or risk factors, ask your clinician what else might help.

Why do labs use different ranges, and what is the 2.07 mg/dL number I see online?

Each lab sets its own range. Mayo Clinic Laboratories lists 1.7–2.3 mg/dL for adults, and a Labcorp sample report lists 1.6–2.3 mg/dL. In 2022 a group of magnesium researchers proposed 2.07 mg/dL (0.85 mmol/L) as a higher lower limit. Most labs haven't adopted it, so use the range on your report first and ask your clinician what it means for you.

How do I convert magnesium between mg/dL and mmol/L?

Multiply mg/dL by 0.411 to get mmol/L, so 2.0 mg/dL is about 0.82 mmol/L. Multiply mg/dL by 0.823 to get mEq/L. To go the other way, multiply mmol/L by 2.43 to get mg/dL.

Can my medicines lower my magnesium?

Some can. Water pills and long-term use of acid-reducing medicines called proton pump inhibitors are linked to lower magnesium, as are a few antibiotics and cancer or transplant medicines. Talk with your clinician before changing any medicine. If your level is low, ask whether a medicine could be involved.

Do I need to prepare for a magnesium blood test?

Usually not. Fasting is only needed if other tests on the same draw require it. Tell your clinician about any supplements, antacids and laxatives you take, since some contain magnesium.

Show the science and sources

Units

  • 1 mg/dL = 1 mg/dL
  • 1 mg/dL = 0.4114 mmol/L
  • 1 mg/dL = 0.8229 mEq/L

Open the Magnesium unit converter

Is a change real?

Magnesium naturally varies about 2.88% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 11% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European Biological Variation Study (EuBIVAS): a summary report.

For clinicians and researchers

About 1% of body magnesium is extracellular, with roughly half in bone and the rest inside cells. Serum magnesium correlates poorly with total body or intracellular content and can be normal despite depleted bone or cell stores, while a markedly low level usually reflects real depletion. Ionized magnesium and RBC magnesium (separate markers) are alternatives with their own limits. Routine methods are colorimetric (xylidyl blue or calmagite dyes). Reference limits vary by lab: Mayo Clinic Laboratories 1.7–2.3 mg/dL (about 0.70–0.95 mmol/L) for adults, Labcorp 1.6–2.3 mg/dL, and the Merck Manual 1.8–2.6 mg/dL (0.74–1.07 mmol/L). In 2022 the MaGNet group (Rosanoff et al.) proposed 0.85 mmol/L (2.07 mg/dL) as the lower limit, citing associations between lower values and cardiovascular and metabolic disease, and compared lab ranges with an independently suggested range of 0.85–0.95 mmol/L. Of 43 reference ranges they collected from 16 countries, only 2 used that cutoff, and they noted that an evidence-based upper limit for hypermagnesemia is still to be set. The Merck Manual defines hypomagnesemia as below 1.8 mg/dL (0.70 mmol/L), with severe cases usually below 1.25 mg/dL (0.50 mmol/L), and hypermagnesemia as above 2.6 mg/dL (1.05 mmol/L). In hypermagnesemia the ECG changes at about 6–12 mg/dL, deep tendon reflexes disappear near 12 mg/dL, and cardiac arrest can occur above about 15 mg/dL. Hypomagnesemia commonly accompanies hypokalemia and hypocalcemia, and it can keep the kidneys wasting potassium until it is corrected. Recognized causes include chronic proton pump inhibitor use (over a year), loop and thiazide diuretics, alcohol use disorder, amphotericin B, cisplatin, cyclosporine and aminoglycosides. ARUP calls results below 1.0 or above 9.0 mg/dL.

LOINC 19123-9 (primary), 2601-3. Specimen: serum-or-plasma.

Sources

  1. Magnesium, Serum (test ID MGS), Mayo Clinic Laboratories (catalog copy hosted by Schneck Medical Center)
  2. Magnesium (test 001537), sample patient report, Labcorp (2018)
  3. Recommendation on an updated standardization of serum magnesium reference ranges, European Journal of Nutrition (MaGNet Global Magnesium Project) (2022)
  4. Critical Values List (CORP-APPEND-0104A, Rev. 46), ARUP Laboratories (2026)
  5. Critical Value Policy, Michigan Medicine Laboratories (MLabs) (2025)
  6. Magnesium (PubChem compound CID 5462224), National Library of Medicine, PubChem
  7. Overview of Disorders of Magnesium Concentration, Merck Manual Professional Version
  8. Hypomagnesemia, Merck Manual Professional Version
  9. Hypermagnesemia, Merck Manual Professional Version
  10. Magnesium blood test, MedlinePlus (US National Library of Medicine)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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