Magnesium (MG)

CPT Code: 



Serum or heparinized plasma 


1 mL 

Minimum Volume: 

0.5 mL 


Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube




Separate serum or plasma from cells within 45 minutes of collection.  Complete clot formation should take place before centrifugation.

Reference Range: 



Temperatures  Period 
Room Temperature  7 Days 
Refrigerated (2-8 ⁰C)  7 Days 
Frozen (≤ -20 ⁰C)  1 Year 



Increased magnesium levels relate mostly to patients in renal failure. Marked increases may be found in such patients who take magnesium salts. Increased serum magnesium is also found with Addison disease and in pregnant patients with severe pre-eclampsia or eclampsia who are receiving magnesium sulfate as an anticonvulsant. Hypermagnesemia may occur in patients using magnesium-containing cathartics.  High magnesium levels are manifested by decreased reflexes, somnolence, and heart block.

Magnesium Deficiency produces neuromuscular disorders. It may cause weakness, tremors, tetany, and convulsions. Hypomagnesemia is associated with hypocalcemia, hypokalemia, long-term hyperalimentation, intravenous therapy, diabetes mellitus, especially during treatment of ketoacidosis; alcoholism and other types of malnutrition; malabsorption; hyperparathyroidism; dialysis; pregnancy; and hyperaldosteronism. Renal loss of magnesium occurs with cis-platinum therapy. Alfrey also adds amphotericin toxicity to the causes of hypomagnesemia.

Causes for Rejection: 

EDTA or citrate plasma specimen 

Interfering Substances: 

Because Mg concentration is 3 times higher in red blood cells than in serum, hemolyzed samples may give spuriously elevated magnesium results.  Bias from hemolysis may vary due to individual sample variations in intracellular magnesium.

EDTA of 200 mg/dL decreases the Mg result by 0.4 mg/dL at a magnesium concentration of 1.8 mg/dL.

Hemoglobin (hemolysate) of 300 mg/dL (monomer) increases a magnesium concentration of 0.94 mg/dL by 18%.

Bilirubin (unconjugated) of 60 mg/dL increases a magnesium concentration of 0.97 mg/dL by 14%.

Lipemia (Intralipid) of 3000 mg/dL increases a magnesium concentration of 0.92 mg/dL by 14%.