Magnesium test explained (Mg)

Only a small part of the body's magnesium is in the blood; most of it is in the bones and inside the cells. Magnesium is needed for energy metabolism, for muscles to relax, for nerve impulses, for heart rhythm and for keeping potassium and calcium in balance. Because of this, a magnesium deficiency often shows up together with low potassium or calcium, and until magnesium is replaced, potassium cannot be restored. Magnesium is regulated by the kidneys and by absorption in the gut, so it is lowered by chronic diarrhoea, alcohol, uncontrolled diabetes and some medicines — especially proton pump inhibitors (used to reduce stomach acid) and diuretics. An excess is rare, mostly in kidney failure or when taking large amounts of magnesium-containing medicines.

• When a doctor suspects a magnesium deficiency or excess — with muscle cramps, weakness, tremor or rhythm disturbances
• Together with low potassium or calcium — a magnesium deficiency is often the cause of those
• During long-term use of proton pump inhibitors or diuretics
• In kidney disease, uncontrolled diabetes, chronic diarrhoea, and with alcohol use
• During pregnancy, when preeclampsia is suspected

High magnesium (hypermagnesaemia) is rare. The most common cause is weakened kidney function, when magnesium is not eliminated — especially while taking magnesium-containing antacids or laxatives. Other causes are adrenal insufficiency, diabetic ketoacidosis, lithium use, dehydration and milk-alkali syndrome.

• Weakened kidney function
• Adrenal insufficiency
• Diabetic ketoacidosis
• Lithium use
• Dehydration
• Milk-alkali syndrome — too much calcium and too many antacids

Symptoms: weakness and drowsiness, nausea, a slowed heart rate and low blood pressure.

What to discuss with a doctor after a high result

• Creatinine and GFR — kidney function
• Magnesium-containing medicines and supplements — antacids, laxatives
• Calcium and potassium — they change together

Low magnesium (hypomagnesaemia) most often arises through loss via the gut or the kidneys: chronic diarrhoea, alcohol, uncontrolled diabetes, diuretics, proton pump inhibitors, some antibiotics and chemotherapy drugs. Other causes are hyperaldosteronism, hypercalcaemia, inflammation of the pancreas, ulcerative colitis and preeclampsia. A deficiency often accompanies low potassium and calcium.

• Alcohol use
• Uncontrolled diabetes
• Chronic diarrhoea, ulcerative colitis
• Medicines: proton pump inhibitors, diuretics, some antibiotics, amphotericin, cisplatin, calcineurin inhibitors
• Hyperaldosteronism
• Hypercalcaemia
• Kidney diseases with magnesium loss
• Inflammation of the pancreas
• Preeclampsia

Symptoms: muscle cramps and tremor, weakness and tiredness, heart rhythm disturbances, irritability and insomnia.

What to discuss with a doctor after a low result

• Potassium and calcium — a lack of them often accompanies a magnesium deficiency and does not recover without magnesium
• Medicines, especially long-term stomach medicines and diuretics
• Alcohol and the state of the gut
• What form to replace it in and how much — the doctor decides, based on the cause and on kidney function

At the Medicina practica laboratory a magnesium test costs from €7 (September 2026 pricing). Magnesium is not in the free diagnostics programme of the National Health Insurance Fund (VLK), which covers lipids, glucose, and heart and cancer markers — the cost depends on the particular institution and on insurance cover.