Serum Magnesium
Also known as: Mg2+, Serum Mg
Magnesium is involved in over 300 enzymatic reactions including ATP production, muscle contraction, and nerve signalling. Deficiency is extremely common but often missed because serum magnesium can remain normal while intracellular stores are depleted.
Venous blood (serum separator tube)
2–4 hours
Not required
Metabolic Panel
Reference Ranges
| Measurement | Reference Range | Unit |
|---|---|---|
| Normal | 1.7 – 2.2 | mg/dL |
Reference ranges are typical adult values. Your laboratory may use slightly different intervals — always use your lab's reported reference.
What This Test Measures
Magnesium is the fourth most abundant cation in the body and the second most abundant intracellular cation (after potassium). Only about 1% is in the serum — the rest is in bone (60%) and inside cells (39%). Serum magnesium reflects the tightly regulated extracellular pool, not the far larger intracellular stores. This means serum magnesium can look normal while tissues are depleted.
When Is This Test Ordered?
- Investigating hypokalaemia (low potassium) — often coexists; cannot correct potassium without replacing magnesium
- Cardiac arrhythmia evaluation
- Alcohol use disorder assessment
- Malabsorption syndromes and inflammatory bowel disease
- Monitoring patients on proton pump inhibitors (long-term PPIs cause hypomagnesaemia)
- Pre-eclampsia treatment monitoring
When Results Are High
Hypermagnesaemia (above 2.5 mg/dL) is almost always from renal failure (kidneys cannot excrete magnesium) or excessive antacid/laxative use. Above 5 mg/dL causes neuromuscular depression; above 7–10 mg/dL risks cardiac arrest.
When Results Are Low
Hypomagnesaemia causes muscle cramps, tremor, cardiac arrhythmias, and seizures. It also makes hypokalaemia and hypocalcaemia treatment-resistant — magnesium depletion must be corrected first. A serum level below 1.5 mg/dL warrants repletion; symptoms can occur at borderline levels (1.5–1.7 mg/dL) when intracellular stores are exhausted.
Factors That Can Affect Your Result
- Long-term proton pump inhibitors (omeprazole, pantoprazole) impair intestinal magnesium absorption
- Alcohol is the most common cause of hypomagnesaemia — increases renal excretion
- Diuretics (loop and thiazide) increase renal magnesium wasting
- Diabetic ketoacidosis causes significant magnesium loss
- Aminoglycoside antibiotics cause renal magnesium wasting
Tracking This Test Over Time
If you have persistent low potassium that does not correct with supplementation, always check and correct magnesium. The kidney cannot conserve potassium in the setting of magnesium deficiency — this is one of the most commonly missed mineral interactions in clinical medicine.
Track your Magnesium in LoomsRelated Tests
Potassium
Potassium is the most important intracellular electrolyte and plays a critical role in heart rhythm and muscle function. Even small deviations outside the reference range can cause life-threatening cardiac arrhythmias.
Calcium
Calcium is tightly regulated by PTH, vitamin D, and calcitonin. Abnormal calcium — whether high or low — can cause symptoms ranging from muscle cramps to kidney stones to cardiac arrhythmias.
Creatinine / eGFR
Creatinine is a waste product filtered by the kidneys; eGFR (estimated glomerular filtration rate) converts it into a percentage of normal kidney function. Together they are the primary tools for detecting and staging chronic kidney disease.
Medical disclaimer
This page is for educational purposes only and does not constitute medical advice. Reference ranges vary between laboratories, and results must be interpreted in the context of your symptoms, history, and other tests. Always discuss your results with your healthcare provider. Content reviewed by the Looms medical team, 2026-06-01.