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Test Code LAB103 Magnesium, Blood

Performing Laboratory

St. Louis Children's Hospital - Chemistry

Specimen Requirements

Patient Preparation: None

Container/Tube  
Preferred: Mint green-top Lithium Heparin (MNTGRN LiHep) tube
Acceptable: Green samplette/microtainer, plain red-top tube, or Gold SST gel tube
Collection Volume: 1.0 mL (minimum 0.6 mL)

Submission Container/Tube: If specimen is coming from outside facility and collected in a microtainer or plain red-top tube aliquot processed sample into a plastic vial for transport (labeling with specimen type).
Special Instructions: None

Sample Rejection

Mislabeled 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: (all ages) 1.4-2.5 mg/dL

Critical Value: <1.0 mg/dL  OR   >4.8 mg/dL

Critical test results will automatically be called back initially and every 24 hours thereafter

Methodology

Colorimetric Endpoint method with Xylidyl blue

Limitations

  • In vary rare cases gammopathy, in particular IgM (Waldenstrom's macroglobulinemia), may cause unreliable results.

For diagnostics purposes, the results should always be assessed in conjunction with the patient's medical history, clinical examination, and other findings.

Additional Information

FOR SLCH CORE LABORATORY USE ONLY

Lab Processing Instructions: Centrifuge specimen to separate. If specimen is collected in a microtainer or plain red-top tube aliquot sample into a Roche false bottom tube for testing (labeling with specimen type)
Processed Volume: 0.3 mL plasma/serum
Analyte Stability:

Specimen Type Temperature Time
Whole Blood (unprocessed)  Ambient 2 days
Plasma/Serum (processed) Refrigerated (preferred)   7 days
  Ambient  2 days
  Frozen  1 month     

Test Classification and CPT Code

83735

LOINC

19123-9

Last Reviewed

06/2025