Preferred Sample Type

Magnesium (serum)

Suitable Specimen Types

  • Serum
  • Li Hep Plasma
1.0 mL blood (Paediatric minium volume 10 uL plasma)

Specimen Transport

Not applicable

Sample Processing in Laboratory

No special requirements

Sample Preparation

Centrifuge sample on arrival

Turnaround Time

1 day

Sample Stability


Magnesium (serum)

General Information

Magnesium is an intracellular cation. It is essential for enzyme activity, for the synthesis of nucleic acids and proteins, and has an important physiological role in the neuromuscular and cardiovascular systems. Total body magnesium is approximately 1000 mmols, of which 60% is in bone, 20% in skeletal muscle, and less than 1% in the extracellular fluid. In the circulation, 65% of serum magnesium is free (ionised), about 20% is protein bound, and the rest is complexed with various anions (eg: phosphate and citrate). The body magnesium balance is regulated by intestinal absorption (predominantly in the ileum and colon), and renal reabsorption (65-75% by the thick ascending loop of Henle, 15-20% in the proximal tubules).

The most commonly used method for assessing magnesium status is serum magnesium concentration.  Spot or 24-hour urine magnesium may be useful in determining renal or intestinal wasting especially in the setting of hypomagnesaemia.

Hypomagnesaemia is common (7-11%) in hospital patients, and the prevalence is higher in critically ill patients. It often coexists with other electrolyte disturbances, especially in the setting of hypokalaemia, hypophosphataemia, hyponatraemia, or hypocalcaemia. Low serum magnesium may be a cause of hypocalcaemia due reduced PTH secretion and activity. Hypermagnesaemia most commonly occurs due to excessive administration of magnesium salts or magnesium-containing drugs (eg: antacids), especially in patients with renal impairment. Mild elevations of serum magnesium are usually asymptomatic. Hypotension and depressed reflexes can be seen with concentrations over 3 mmol/L. Very high serum magnesium concentrations are usually iatrogenic with serum levels > 4mmol/L associated with paralysis, hypotension, bradycardia, cardiac arrest.

Patient Preparation



Haemolysed samples are unsuitable for magnesium analysis

Reference Range

Neonate (<4wks)   0.6-1.0 mmol/L

4wks - 16yrs         0.7-1.0 mmol/L

Adult                    0.7-1.0 mmol/L

(Source : Pathology Harmony Recommendations)


  • EQA Scheme?: Yes
  • EQA Status:

    UK NEQAS Clinical Chemistry scheme

The laboratories at Heartlands Hospital, Good Hope Hospital and Solihull Hospital form part of the services provided by University Hospitals Birmingham and are UKAS (United Kingdom Accreditation Service) accredited to the ISO 15189:2012 standard. For a list of accredited tests and other information please visit the UKAS website using the following link:

  • Heartlands, Good Hope and Solihull Hospital pathology laboratories are a UKAS accredited medical laboratory No.8217
  • United Kingdom Health Security Agency laboratory is a UKAS accredited medical laboratory No.8213

Tests not appearing on the UKAS Schedule of Accreditation currently remain outside of our scope of accreditation. However, these tests have been validated to the same high standard as accredited tests and are performed by the same trained and competent staff.

For further test information, please visit the test database:

For further information contact Louise Fallon, Quality Manager, 0121 424 1235