Magnesium

Background

Half of the total body magnesium is found in the bone and is deposited and reabsorbed along with calcium. Like calcium about 30% is bound to albumin whilst the rest is freely filtered at the kidney and then reabsorbed along the tubule. Hypomagnesaemia is usually caused by increased loss (diarrhoea, renal disease) rather than decreased intake (malabsorption, parenteral feeding). Symptoms of low magnesium mimic those of hypocalcaemia and will often cause a low calcium by possibly inhibiting calcium response to Vitamin D. Hypermagnesaemia is very rare.

Reference ranges

Serum/Plasma: 0.7 – 1.0 mmol/L
Urine: 3.00 – 5.00 mmol/24hour

Specimen requirements

Magnesium
Sample type:

• Serum
• Lithium Heparin Plasma

or

• Plain Urine

Magnesium Urine
Sample type:

• Plain 25mL Universal Urine Container

Sample identification:

• Three patient identifiers from
  • Name
  • D.O.B.
  • Address
  • N.H.S. number
  • Unit Number
  should match on the specimen and request form. This check may be performed prior to centrifugation by the Central Sort department.

Turnaround time

2 hours