Magnesium

Magnesium is a cofactor for hundreds of enzymes — ATP biology, protein synthesis, nerve transmission, vascular tone. Only about 1% of body magnesium is in serum, so a normal serum level doesn't rule out tissue deficiency; conversely, when serum magnesium IS low, total-body deficiency is usually severe. Magnesium status quietly influences whether potassium and calcium can be corrected effectively — magnesium-deficient patients have refractory hypokalaemia and hypocalcaemia until magnesium is replaced.

• Adults: about 1.7-2.2 mg/dL (0.7-0.95 mmol/L), similar across sexes and adult ages.
• Serum reflects only about 1% of the body's magnesium, so a normal value can still hide tissue deficiency.

Your lab's printed range is what counts - assays and units differ.

• Renal failure — magnesium accumulates without normal renal excretion.
• Magnesium-containing antacids and laxatives in patients with reduced renal function.
• Iatrogenic — eclampsia/pre-eclampsia treatment with magnesium sulfate.

• Gastrointestinal loss — chronic diarrhoea, malabsorption, proton-pump inhibitor use, gastric bypass.
• Renal loss — diuretics (loop and thiazide), alcohol, aminoglycoside antibiotics, cisplatin.
• Reduced intake — alcoholism, refeeding syndrome.
• Hypoparathyroidism, diabetes.
• Look for low magnesium whenever low potassium or calcium is refractory to replacement.

• Low magnesium: muscle cramps and twitches, tremor, fatigue, palpitations; when severe, numbness or seizures. Often silent until marked.
• High magnesium (usually with kidney impairment): weakness, nausea, low blood pressure, drowsiness.
• Symptoms overlap with low potassium and calcium, which magnesium deficiency often accompanies.