Magnesium, Urine

Magnesium excretion controls magnesium balance.1 Magnesium urinary excretion is enhanced by increasing blood alcohol levels, diuretics, Bartter syndrome, corticosteroids, cis-platinum therapy and aldosterone. Renal magnesium wasting occurs in renal transplant recipients who are on cyclosporine and prednisone.2 Renal conservation of magnesium is diminished by hypercalciuria, salt-losing conditions, and the syndrome of inappropriate secretion of antidiuretic hormone.1 Magnesium deficiency is often inadequately documented by serum magnesium levels. Urinary magnesium analyses have been advocated before and after therapeutic magnesium administration to further investigate the significance of an apparent low serum magnesium.3

Methodology: Atomic absorption spectrometry (AAS) or colorimetric

Reference Interval:

Environmental exposure: 12.0−293.0 mg/24 hours

Additional Information: Hypercalcemia, hypophosphatemia and acidosis are among inhibitors of tubular reabsorption of magnesium.2

Footnotes: 1. Alfrey AC. Disorders of magnesium metabolism. In: Schrier RW, ed. Renal and Electrolyte Disorders. 2nd ed. Boston, Mass: Little, Brown and Co;1980: 299-319.

2. Barton CH, Vaziri ND, Martin DC, Choi S, Alikhani S. Hypomagnesemia and renal magnesium wasting in renal transplant recipients receiving cyclosporine. Am J Med. 1987 Oct; 83(4):693-699. PubMed 3314493

3. Chernow B, Bamberger S, Stoiko M, et al. Hypomagnesemia in patients in postoperative intensive care. Chest. 1989 Feb; 95(2):391-397. Erratum: 1989 Jun; 95(6):1362. PubMed 2914492