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HelpTest Code LAB406 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
Special Instructions
Method Name
Colorimetric Endpoint Assay
Specimen Type
UrineNecessary 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 |
Reject Due To
| All specimens will be evaluated at Mayo Clinic Laboratories for test suitability. |
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.
Method Description
In alkaline solution, magnesium forms a purple complex with xylidyl blue, diazonium salt. The magnesium concentration is measured photometrically via the decrease in xylidyl blue absorbance.(Package insert: Roche MG2 kit. Roche Diagnostics;Â V8.0 01/2020)
Specimen Retention Time
7 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
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.
Secondary ID
610768Day(s) Performed
Monday through Sunday