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Test Code MAGU Magnesium, 24 Hour, Urine

Useful For

Assessing the cause of abnormal serum magnesium concentrations using a 24-hour urine collection

 

Determining whether nutritional magnesium loads are adequate

 

Calculating urinary calcium oxalate and calcium phosphate supersaturation and assessing kidney stone risk

Method Name

Colorimetric Endpoint Assay

Reporting Name

Magnesium, 24 HR, U

Specimen Type

Urine


Necessary Information


Specimen volume in milliliters and duration are required.



Specimen Required


Supplies: Sarstedt 5 mL Aliquot Tube (T914)

Collection Container/Tube: 24-hour graduated urine container with no metal cap or glued insert

Submission Container/Tube: Plastic, 5 mL tube or a clean, plastic urine container with no metal cap or glued insert

Specimen Volume: 4 mL

Collection Instructions:

1. Collect urine for 24 hours.

2. Refrigerate specimen within 4 hours of completion of 24-hour collection.

Additional Information: See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens for multiple collections.


Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Refrigerated (preferred) 14 days
  Frozen  30 days
  Ambient  72 hours

Reference Values

51-269 mg/24 hours

Reference values have not been established for patients <18 years and >83 years of age.

Interpretation

Urinary magnesium excretion should be interpreted in concert with serum concentrations.

 

In the presence of hypomagnesemia, a 24-hour urine magnesium greater than 24 mg/day or fractional excretion greater than 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.

Clinical Reference

1. Delaney MP, Lamb EJ: Kidney disease. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. 2018:1309

2. Al Ghamdi SM: Magnesium deficiency: pathophysiologic and clinical overview. Am J Kidney Dis. 1994;24(5):737-752

3. Sutton RA: Abnormal renal magnesium handling. Miner Electrolyte Metab. 1993;19(4-5):232-240

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

83735

LOINC Code Information

Test ID Test Order Name Order LOINC Value
MAGU Magnesium, 24 HR, U 24447-5

 

Result ID Test Result Name Result LOINC Value
MG24 Magnesium, 24 HR, U 24447-5
TM115 Collection Duration 13362-9
VL111 Urine Volume 3167-4

Forms

If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.

Day(s) Performed

Monday through Sunday

Report Available

Same day/1 to 3 days