Magnesium

Mg, Magnesium, Blood Level, MAG

Test Codes

EPIC: LAB103

Department

Chemistry

Specimen Collection Criteria

FOR EC AND INPATIENT SAMPLE COLLECTION ONLY:

Preferred Sample:  One Light Green (Mint)-top Plasma Separator Tube (PST). (Minimum Whole Blood: 4.0 mL) 

Acceptable Sample:  One Gold-top SST (Minimum Whole Blood: 4.0 mL) 

Do NOT use Dark Green-top Lithium or Sodium Heparin tubes.

FOR PHYSICIAN OFFICE/OUTREACH SAMPLE COLLECTION:

COLLECT:  One Gold-top SST (Minimum Whole Blood: 4.0 mL)  

Contact the Laboratory for the acceptability of other tube types.
See Minimum Pediatric Specimen Requirements for Microtainer^® collection.

Physician Office/Draw Specimen Preparation

Let SST specimens clot for 30-60 minutes then immediately centrifuge to separate serum from cells. Refrigerate (2-8°C or 36-46°F) the centrifuged SST tube within two hours of collection. (Minimum: 0.5 mL)

Preparation for Courier Transport

Transport: Centrifuged SST tube refrigerated (2-8°C or 36-46°F). (Minimum: 0.5 mL)

Rejection Criteria

• Moderate to grossly hemolyzed specimens.
• Red-top tubes with serum not separated from cells within two hours of collection.

In-Lab Processing

Let SST specimens clot 30-60 minutes. Centrifuge SST tubes or Microtainers^® to separate serum from cells. Deliver immediately to the appropriate testing station.

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes and Microtainers^® without Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 4 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 7 days

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 5 days

Laboratory

Canton Chemistry Laboratory
Dearborn Chemistry Laboratory
Farmington Hills Chemistry Laboratory 
Grosse Pointe Chemistry Laboratory 
Lenox Chemistry Laboratory
Livonia Chemistry Laboratory
Royal Oak Automated Chemistry Laboratory 
Troy Chemistry Laboratory
Taylor Chemistry Laboratory
Trenton Chemistry Laboratory
Wayne Chemistry Laboratory 

Performed

Sunday – Saturday, 24 hours a day.
STAT results available within 1 hour after receipt in Chemistry Laboratory.
Routine results available within 4 hours.

Reference Range

1.7-2.5 mg/dL.

Test Methodology

Enzymatic.

Interpretation

• Most magnesium in the body is present within cells, therefore serum magnesium may not accurately reflect total body magnesium stores. Serum magnesium is, however, the most readily available laboratory test.
• Magnesium may be increased in patients who are taking magnesium-containing antacids or cathartics, pregnant patients being treated for pre-eclampsia or eclampsia, in renal failure and in Addison's disease.
• Magnesium may be decreased in patients on long-term IV therapy or hyperalimentation, diabetes mellitus (especially during treatment of diabetic ketoacidosis), conditions of malabsorption and chronic diarrhea, hyperaldosteronism, pregnancy and in patients on dialysis. Hypomagnesemia may produce neuromuscular spasm, tetany and convulsions and cardiac arrhythmias. Since magnesium is necessary for parathyroid hormone release and action, hypomagnesemia may be associated with hypocalcemia.

Clinical Utility

The quantitation of magnesium aids in the investigation of unexplained hypocalcemia, in the management of patients following cardiac surgery or those with cardiac arrhythmias, and in the management of patients being treated for pre-eclampsia or eclampsia. An association between severe hypomagnesemia and aminoglycoside therapy has been described.

CPT Codes

83735

Contacts

Last Updated

8/4/2025