Sodium (and urine)

Background

Sodium is the most abundant extracellular cation, and for this reason it and its associated anions account for most of the activity of the extracellular fluid. The clinical symptoms of disturbances of sodium concentration are due to changes in osmolality. This concentration is also linked to the total amount of water as well as the amount of ion, therefore there is a close link between the homeostatic mechanisms for sodium and water.

Hyponatraemia causes cellular overhydration leading to clinical symptoms of headache, confusion and fits. Hypernatraemia causes cellular dehydration and thirst, on the cerebral cells this leads to confusion followed by coma.

Sodium measurements are used in the diagnosis and treatment of gross changes in water and salt balance, aldosteronism, diabetes insipidus, adrenal hypertension, Addison’s disease, dehydration, inappropriate antidiuretic hormone secretion, diabetic acidosis, severe diarrhoea, or other diseases involving electrolyte imbalance.

Reference ranges

Serum: 133 – 146 mmol/L
Urine: 40 – 220 mmol/24 hours

Specimen requirements

Sample type:

• Serum
• Lithium Heparin Plasma
  or
• Plain Urine (random or 24 hour)

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