Sodium (Blood)

Diagnostic Use

Increased sodium concentrations may be seen in:

• dehydration
• diarrhoea
• vomiting
• excessive sweating
• diabetes insipidus

Decreased sodium concentrations may be seen in:

• SIADH
• diuretics
• Adrenocortical insufficiency , salt-losing congenital adrenal hyperplasia
• cardiac failure
• cirrhosis
• diarrhoea, ileostomy
• renal impairment (salt-losing forms)

Interpretation

• CORRECTED SODIUM

  Sodium Correction for Abnormal Protein or Triglyceride

  In patients with hyperproteinaemia or hypertriglyceridaemia, the serum sodium measured by laboratory analysers is artefactually decreased due to the “electrolyte exclusion effect”. This is known as pseudohyponatremia. Sodium is present only in the water phase of serum; therefore an increased fat or protein phase (lower volume of water phase) means that the sodium concentration measured per litre of serum will be low.

  Conversely, in patients with hypoproteinaemia, serum sodium measured using laboratory analysers is falsely increased.

  NOTE: This effect does not apply to sodium measured using a blood gas analyser.

  Hypertriglyceridaemia (lipemia): The lipoproteins can be removed by high speed centrifugation, and the sodium analysis repeated to obtain a true sodium concentration.

  Hyperproteinaemia: The plasma sodium can be corrected using the formula:

  Corrected sodium = measured sodium + [ (total protein – 70) / 10]

   

  Hypoproteinaemia: This can be corrected using the formula:

  Corrected sodium = measured sodium – [(70 – total protein)/10]

  Total Protein (g/L)	Na (mmol/L) to be added or subtracted
  30	-4
  40	-3
  50	-2
  70	0
  90	+2
  110	+4
  130	+6

Reference Intervals