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Test Code MAGNR Magnesium, Random, Urine

Reporting Name

Magnesium, Random, U

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful For

Assessing the cause of abnormal serum magnesium concentrations


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

Specimen Type


Specimen Required

Collection Container/Tube: Plastic urine container

Submission Container/Tube: Plastic, 5-mL tube (T465) or a clean, plastic aliquot container with no metal cap or glued insert

Specimen Volume: 4 mL

Collection Instructions:

1. Collect a random urine specimen.

2. No preservative.

Specimen Minimum Volume

1 mL

Specimen Stability Information

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

Reject Due To

All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

Reference Values

Random Magnesium/Creatinine Ratio: ≥0.035 mg/mg


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


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

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

Day(s) and Time(s) Performed

Monday through Sunday; Continuously.

Test Classification

This test has been modified from the manufacturer’s instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
MAGNR Magnesium, Random, U 19124-7


Result ID Test Result Name Result LOINC Value
MGCO Magnesium, Random, U 19124-7
CREA7 Creatinine Concentration 2161-8
MCTR Magnesium/Creatinine Ratio 13474-2