Is magnesium included in a standard metabolic panel?

Not always. Serum magnesium is frequently not part of standard metabolic panels and often needs to be requested specifically, particularly when deficiency or an electrolyte disturbance is suspected.

How long does it take to get magnesium results through Access Medical Laboratories?

Results are typically available within 1–3 business days from specimen receipt at the processing laboratory.

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Magnesium (Serum) Test

Q: Why is magnesium checked in refractory low potassium or calcium?

Hypomagnesaemia frequently accompanies and perpetuates hypokalaemia and hypocalcaemia, which often fail to correct until magnesium is repleted. Magnesium should therefore be measured and corrected in refractory cases.

Q: What medications can lower magnesium?

Loop and thiazide diuretics, proton-pump inhibitors, aminoglycosides, and cisplatin increase renal or gastrointestinal magnesium loss and can lower serum magnesium over time. Medication history should be documented.

Q: Is fasting required for the magnesium test?

No. Fasting is not required. However, recent magnesium supplementation, antacids, or laxatives should be documented, as they transiently raise levels and may mask depletion.

Q: Why can haemolysis affect magnesium results?

Magnesium is concentrated within red cells, so a haemolysed specimen releases intracellular magnesium and spuriously raises the serum value. Specimens should be handled to avoid haemolysis.

Q: What causes a high serum magnesium?

Hypermagnesaemia is most often due to renal impairment or magnesium-containing medications in the setting of reduced clearance. Significant elevations can cause neuromuscular and cardiac depression.

The serum magnesium test measures circulating magnesium, the standard index of magnesium status and an essential cofactor in neuromuscular, cardiac, and metabolic function. It detects hypomagnesaemia and hypermagnesaemia and investigates refractory hypokalaemia and hypocalcaemia, which often fail to correct until magnesium is repleted.

Biomarkers

Blood (serum)

Sample

1–3 business days

Turnaround

No — however, recent magnesium supplementation, antacids, or laxatives should be documented as they transiently raise levels

Fasting

What is the Magnesium test?

The Magnesium Test measures serum magnesium, the standard index of magnesium status and an essential cofactor in neuromuscular, cardiac, and metabolic function. It is ordered to detect and monitor hypomagnesaemia and hypermagnesaemia and to investigate electrolyte disturbances that magnesium deficiency commonly underlies. Within electrolyte and mineral assessment, serum magnesium is the routine first-line measure, although it reflects only the small circulating fraction rather than total body stores. It is particularly relevant in refractory hypokalaemia and hypocalcaemia, which often fail to correct until magnesium is repleted, and in patients on magnesium-wasting drugs, with gastrointestinal losses, or with renal impairment that risks accumulation. More specialised measures such as red-cell or ionised magnesium and the magnesium loading test are reserved for cases where deficiency is suspected despite normal serum values, but serum remains the clinical standard.

What does the Magnesium test measure?

Mg(Magnesium (Serum))

Range: 1.7–2.4 mg/dL (0.70–0.99 mmol/L) # REVIEWER FLAG: Reference interval is assay-dependent — reviewer to confirm against Access Medical Laboratories' assay-specific range.Optimal: Many practitioners target the upper half of the reference range (≥2.0 mg/dL) as functionally optimal # REVIEWER FLAG: Functional 'optimal' magnesium target is not standardised — reviewer to confirm against IFM or equivalent source.mg/dL / mmol/L

Magnesium is the second most abundant intracellular cation and an essential cofactor for over 300 enzymatic reactions, including ATP-dependent processes, neuromuscular conduction, and the maintenance of potassium and calcium homeostasis. The overwhelming majority of body magnesium resides in bone and soft tissue, with less than 1% in serum, so the circulating concentration is tightly regulated by renal handling but is an insensitive index of total body stores. Serum magnesium exists in protein-bound, complexed, and free ionised fractions, the last being the physiologically active form.

Serum magnesium is the standard, widely available measure of magnesium status and is used to detect and monitor hypomagnesaemia and hypermagnesaemia. Because most magnesium is intracellular, a normal serum value does not exclude tissue depletion, and clinically significant deficiency can exist with borderline-normal serum levels. It is most useful in patients with relevant symptoms, electrolyte disturbances (especially refractory hypokalaemia or hypocalcaemia), or conditions and drugs that deplete magnesium.

Why is the Magnesium test ordered?

Investigation of suspected hypomagnesaemia — neuromuscular irritability, tremor, tetany, or unexplained arrhythmia
Evaluation of refractory hypokalaemia or hypocalcaemia, which frequently fail to correct until magnesium is repleted
Assessment of patients on magnesium-wasting medications — loop or thiazide diuretics, proton-pump inhibitors, aminoglycosides, or cisplatin
Monitoring of patients with gastrointestinal losses — chronic diarrhoea, malabsorption, or short bowel syndrome — at risk of depletion
Surveillance for hypermagnesaemia in renal impairment or in patients receiving magnesium-containing preparations
Evaluation of arrhythmia or QT prolongation where magnesium status is clinically relevant
Comprehensive micronutrient and metabolic assessment alongside calcium, potassium, and vitamin D

Sample collection and turnaround

Sample type

Blood (serum)

Fasting required

No — however, recent magnesium supplementation, antacids, or laxatives should be documented as they transiently raise levels

Collection method

Venipuncture at patient service centre

Turnaround

1–3 business days

Collection notes

Handle the specimen carefully to avoid haemolysis, which spuriously raises magnesium. Document magnesium supplementation, magnesium-containing antacids or laxatives, and relevant medications.

Specimen requirements

Minimum 0.5 mL serum, non-haemolysed. Separate serum from cells per Access Medical Laboratories protocol. Specimen stable refrigerated; follow Access Medical Laboratories transport guidelines.

What can affect Magnesium results?

elevatesHaemolysis of the specimen

Magnesium is concentrated within red cells, so haemolysis releases intracellular magnesium and spuriously raises the serum result. Specimens should be handled to avoid haemolysis.

elevatesRenal impairment

The kidneys are the principal route of magnesium excretion, so reduced renal function raises serum magnesium and predisposes to hypermagnesaemia, particularly with magnesium-containing medications.

reducesMagnesium-wasting medications (diuretics, PPIs, aminoglycosides, cisplatin)

These drugs increase renal or gastrointestinal magnesium loss, lowering serum magnesium over time. Medication history should be documented when interpreting a low result.

variableIntracellular distribution and normal serum despite depletion

Because under 1% of body magnesium is in serum, total-body depletion can coexist with a normal or borderline serum value, so a normal result does not exclude deficiency.

elevatesRecent magnesium supplementation or antacids

Oral or intravenous magnesium and magnesium-containing antacids or laxatives transiently raise serum levels and may mask an underlying deficit. Recent intake should be recorded.

variableAcid-base disturbances and insulin/glucose shifts

Shifts of magnesium between intracellular and extracellular compartments, as with insulin administration or correction of acidosis, can transiently alter serum magnesium independent of total stores.

What do Magnesium results mean?

Elevated

Hypermagnesaemia is most often iatrogenic or due to renal impairment, arising from magnesium-containing medications in the setting of reduced clearance. Significant elevations can cause neuromuscular and cardiac depression and warrant review of magnesium intake and renal function.

Normal

A normal serum magnesium does not exclude total-body depletion, because the circulating fraction is small and tightly regulated. Where deficiency is strongly suspected despite a normal value, red-cell or ionised magnesium or a magnesium loading test may be considered.

Reduced

Hypomagnesaemia commonly results from gastrointestinal or renal losses, drugs, or malnutrition. It frequently accompanies and perpetuates refractory hypokalaemia and hypocalcaemia, so magnesium should be checked and repleted when these fail to correct.

Note: Serum magnesium is an insensitive marker of total body stores, so clinically significant deficiency can exist with borderline-normal levels. Haemolysis falsely elevates results, recent supplementation can mask depletion, and renal function strongly influences levels. Interpret alongside potassium, calcium, renal function, and the medication history.

Frequently asked questions

No. Under 1% of body magnesium is in serum and the level is tightly regulated, so total-body depletion can coexist with a normal or borderline-normal serum value. Red-cell or ionised magnesium may be considered when deficiency is strongly suspected.

How to access the Magnesium test

The Magnesium reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.

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About this page

Published: June 2, 2026

Last reviewed: June 2, 2026

References:

This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.

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