What is a magnesium test?
Serum magnesium measures Mg2+ in your blood. About 50-60% of body magnesium is stored in bone; only 1% is in blood, making serum levels an imperfect but practical indicator. Magnesium is essential for ATP energy production, nerve and muscle function, blood glucose control and blood pressure regulation.
Magnesium normal range
| Category | mg/dL | mmol/L |
|---|---|---|
| Normal | 1.7 – 2.3 | 0.70 – 0.95 |
| Low (hypomagnesaemia) | < 1.7 | < 0.70 |
| Critical low | < 1.0 | < 0.41 |
| High (hypermagnesaemia) | > 2.3 | > 0.95 |
LOW Magnesium — Hypomagnesaemia
Estimated to affect up to 45% of the population. Common causes: poor diet, alcohol excess, prolonged diarrhoea, type 2 diabetes (insulin resistance increases urinary Mg loss), loop diuretics (furosemide), and long-term PPI use (omeprazole blocks intestinal Mg absorption). Symptoms: muscle cramps, tremors, fatigue, insomnia, anxiety, irregular heartbeat, seizures. Critical insight: low magnesium causes refractory hypocalcaemia and hypokalaemia that cannot be corrected until magnesium is replaced first.
HIGH Magnesium — Hypermagnesaemia
Almost always caused by taking too much magnesium (supplements, antacids) combined with kidney disease. Mild: nausea. Higher levels: loss of deep tendon reflexes, low blood pressure, bradycardia, breathing difficulty. Very high: cardiac arrest. Treatment: stop magnesium, IV calcium gluconate, dialysis if severe.
Questions to ask your doctor
- Is my PPI or diuretic causing low magnesium?
- Should I take a magnesium supplement?
- Which magnesium form is best absorbed (glycinate, malate, citrate)?
- Is this why my calcium and potassium stay low?