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Test Code LAB406 Magnesium, Urine, 24 Hour

Performing Laboratory

St. Louis Children's Hospital Laboratory - Chemistry

Specimen Requirements

Patient Preparation: None

Collection Container/Tube:

Preferred: Plain, brown 24-hour urine collection container with or without preservatives (if collected without preservative, must stay refrigerated)

Specimen Collection Volume: Entire urine specimen collected over 24 hour period

Submission Container/Tube: If specimen is coming from outside facility, mix well and measure total volume before making aliquot with a minimum of 1.0 mL of urine into a plastic screw-capped tube for transport labeling with volume and duration times as well as if collected with preservative (or send entire 24-hr urine jug).

Special Instructions: 

  1. Refrigerate specimen during collection
  2. Note collection start and stop dates and times on collection container
  3. Call lab at 314-454-4268 to obtain 24-hour collection jug if needed
  4. Follow instructions on "Urine Collection"

 

Sample Rejection

Mislabled or unlabeled specimens

Logistics

Test Availability: Monday-Sunday

Cut-off time: None, performed as received

Turnaround Time: Same Day; 2 hours from receipt in performing lab

Reference Values

Reference Interval: 

<18 years: No reference ranges established                                     
>or = 18 years: 70.0-150.0 mg/24hr

Critical Value: None established

 

Methodology

Colorimetric Endpoint

Limitations

  • NA

Additional Information

FOR SLCH CORE LABORATORY USE ONLY

Lab Processing Instructions: Mix well and measure total volume collected. If specimen collected without acid preservative, make aliqout with minimum of 1.0 mL urine. pH urine to <1 with concentrated HCL. Centrifuge the pH'd urine to clear any precipatates aliquoting cleared urine into a Roche-false bottom tube for testing. Label pH on aliqout tube.

Processed Volume: minimum 0.3 mL urine

Analyte Stability:

Specimen Type Temperature Time
urine (without preserative)    Ambient or refrigerated    4 hours
urine (with preservative)     Ambient 2 days  
  Refrigerated     3 days   
  Frozen  1 year      

 

NOTE: 

  1. Total volume of specimen collected and collection duration period is required. Note this information on the aliquot container label and into LIS system
  2. If floor calls for collection container with preservative, add 5 mL of 6 mol/L HCL to 24-hr jug and label container as containing acid.
  3. if collection duration is <18 hours or >30 hours cancel the 24Hr orderable and re-order test using the Timed orderable.

Test Classification and CPT Code

83735

LOINC

Mg 24Ur:       24447-5

Volume Ur:    19153-6

Duration:        13362-9

Last Reviewed

07/2025