Magnesium, Urine

CPT: 83735
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Test Details

Use

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

Specimen Requirements

Specimen

Urine (24-hour)

Volume

5 mL

Minimum Volume

2.2 mL

Container

Plastic urine container with 10 mL 6N HCl

Collection

Instruct the patient to void at 8 AM and discard the specimen. Then collect all urine including the final specimen voided at the end of the 24-hour collection period (ie, 8 AM the next morning). Screw the lid on securely. Transport the specimen promptly to the laboratory. Container must be labeled with patient's full name, room number, date and time collection started, and date and time collection finished.

Storage Instructions

Refrigerate (KBS tablet is acceptable).

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

No preservative in the collection container; presence of blood in the urine; improper labeling

Clinical Information

Special Instructions

The test request form must state 24-hour collection volume. After collection, pH is adjusted to 1.5 to 2.0 with 6N HCl.

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. 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):1362.2914492

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
003400 Magnesium, Urine 013730 Magnesium, U mg/dL 19124-7
003400 Magnesium, Urine 013805 Magnesium,Urine 24hr mg/24 hr 24447-5

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