diagnosis of cause of hyponatraemia

Last reviewed 04/2022

A definitive diagnosis of the underlying aetiology of hyponatraemia is not always possible at the time of initial presentation

  • an accurate history should be taken
    • look for signs and symptoms of hyponatraemia
    • inquire about any medication (e.g. - diuretics, antidepressants), recently received intravenous fluids, vomiting, diarrhea and about any associated diseases   (1)
  • measure serum osmolality (2)
    • if serum osmolality is normal (275 – 295 mOsmol/l) or high (>295 mOsmol/l) consider causes such as hyperglycaemia, hyperlipidaemia, hyperprotinaemia and renal failure
    • in cases of low osmolality    (<275 mOsmol/l) assess volume status of the patient,
      • hypovolaemia – tachycardia, postural hypotension, dry skin, reduced skin turgor, raised blood urea, raised plasma rennin
      • euvolaemia – blood urea normal or slightly reduced
      • hypervolaemia – oedema (peripheral, sacaral, pulmonary), ascites, increased JVP or CVP (3)
  • the three major classifications of hypotonic hyponatraemia based on the patient?s ECF volume status:
    • hypovolaemic hyponatraemia
    • normovolaemic (euvolaemic) hyponatraemia
    • hypervolaemic hyponatraemia
  • plasma glucose and lipids, renal function, thyroid function and adrenal function test should be done if clinically indicated (1,2)