Magnesium is an essential nutrient which is involved in many biochemical functions. It has a structural role in nucleic acids and ribosomal particles, required as an activator for many enzymes and has a role in energy producing oxidative phosphorylation.
The normal body contains between 21 to 28 g magnesium, more than 50% of which is complexed with calcium and phosphate in bone. Only approximately 1% of the total magnesium is found in the extracellular fluid; hence, it tends to enter and leave cells under the same conditions as potassium. Approximately 35% of plasma magnesium is protein-bound, mainly to albumin, and therefore changes in albumin concentration may affect magnesium.
Hypomagnesemia results in the impairment of neuromuscular function and may develop in severe prolonged diarrhea, malabsorption syndromes, hyperaldosteronism, and diuretic therapy. Hypermagnesemia is seen in renal glomerular failure and diabetic coma.
Urinary magnesium excretion should be interpreted in concert with serum concentrations.
In the presence of hypomagnesemia, a 24-hour urine magnesium >24 mg/day or fractional excretion >0.5% suggests renal magnesium wasting. Lower values suggest inadequate magnesium intake and/or gastrointestinal losses.
In the presence of hypermagnesemia, urinary magnesium levels provide an indication of current magnesium intake.
Lower urinary magnesium excretion increases urinary calcium oxalate and calcium phosphate supersaturation and could contribute to kidney stone risk.