Magnesium, Urine

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Subject: Magnesium, Urine

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Definition

  • Magnesium is an important but commonly neglected electrolyte. 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 apparent low serum magnesium. Abnormal levels of magnesium are most frequently seen in conditions or diseases that cause impaired or excessive excretion of magnesium by the kidneys or that cause impaired absorption in the intestines. Magnesium levels may be checked as part of an evaluation of the severity of kidney problems and/or of uncontrolled diabetes and may help in the diagnosis of GI disorders. Renal magnesium wasting occurs in renal transplant recipients who are on cyclosporine and prednisone. Renal conservation of magnesium is diminished by hypercalciuria, salt-losing conditions, and the SIADH.

  • Normal range:

    • Twenty-four–hour urine: 72–120 mg/day

    • Random urine:

      • Male: 18–110 mg/g creatinine

      • Female: 14–139 mg/g creatinine

Use

  • Investigate chronic pancreas inflammation

  • Decreased blood magnesium

Interpretation

Increased In

  • Alcohol

  • Diuretics

  • Bartter syndrome

  • Corticosteroids

  • Cisplatin therapy

  • Aldosterone

Decreased In

  • Insufficient magnesium intake

  • Extrarenal loss

Limitations

  • Magnesium forms insoluble complexes with normal urine constituents that precipitate as soon as urine is passed. Acidification is not required.

  • Urine concentration is diet dependent.

  • Magnesium depletion could be common condition found in 26% of hospitalized patients.

  • High concentrations of gadolinium are known to interfere with most metals tests.

 
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