Turnaround Time: 1-3 days
CPT Code:


Test Type: Urine. 24 Hour 5mL


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


Collection Details:

Collection Instructions:

Specimen: Urine (24-hour)

Volume: 5 mL

Minimum Volume: 2.2 mL (Note: This volume does not allow for repeat testing.)

Container: Plastic urine container with 30 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: Room temperature (KBS tablet is acceptable)

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.