Plasma
Urine
Adult patient:
Heparin gel tube
Minimum blood volume: 5 mL
Plain bottle
Minimum volume: 10 mL
24 Hr urine:
Paediatric patient:
Paediatric heparin tube
Number of vials: 1
Minimum blood volume: 1.3 mL
Authorisation code required
No
24 Hr available service
Yes
(Call extension: 3353 for express result)
No
Method
Spectrophotometry
Reference interval
| Plasma: | 0.66 - 1.07 mmol/L |
| Urine: | 3.3 - 4.9 mmol/day |
(Source: Robert WL et al. Reference Information for the Clinical Laboratory. In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 4th Edn. Burtis CA, Ashwood ER, Bruns DE eds. Elsevier Saunders 2006)
Clinical indication
Plasma:
Detection of hypomagnesaemia as the cause of unexplained cardiac
arrhythmias, neuromuscular disorders, refractory hypocalcaemia
Assessment of patients with clinical features suggesting hypocalcaemia and a normal plasma calcium, or with refractory hypocalcaemia / hypokalaemia
Hypermagnesaemia may occur in renal failure, but assessment is rarely required.
Monitoring magnesium sulphate anticonvulsant therapy or therapy causing renal magnesium loss (e.g. cisplatinum).
24 Hr urine:
Confirmation of suspected urinary magnesium loss
Result interpretation
Plasma:
Decreased levels may be due to increased renal or gastrointestinal loss, or to decreased intake.
Levels fall rapidly in response to reduced intake and may not reflect tissue levels.
Hypomagnesemia is associated with hypocalcemia, alcoholism, some types of malnutrition, malabsorption, chronic haemodialysis, and pregnancy.
Increased serum magnesium concentrations occur in patients with renal failure, dehydration, and Addison's disease.
24 Hr urine:
Decreased urinary magnesium in a patient with hypomagnesaemia indicates a non-renal cause.
Measurement of uncertainty
Frequency of measurement
Daily