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Clinical features

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Symptoms depend on the severity of hyponatraemia and the rate of decrease in the plasma sodium concentration (1).

  • hyponatraemia is usually asymptomatic when plasma sodium is between 130-135mmol per litre (1).
  • features of severe hyponatraemia may occur when the plasma sodium falls rapidly towards 125 mmol/l and symptoms usually appear when the sodium level is below 115 mmol/l (2).

Signs and symptoms of hyponatraemia are often initially non specific (3)

  • the symptoms may range from lethargy and anorexia to agitation, disorientation, seizures and coma
  • cerebral oedema may be seen in acute onset of hyponatraemia (3)

Features of moderately severe hyponatraemia i.e. plasma sodium less than 120 mmol/l):

  • headache, nausea, vomiting
  • malaise, irritability, depression, personality change
  • cramps, muscle weakness

Features of severe hyponatraemia i.e. plasma sodium less than 110 mmol/l):

  • confusion, drowsiness, convulsions
  • diminished reflexes, extensor plantar response
  • Cheyne-Stokes respiration (3)
  • coma, death

Patients with chronic hyponatraemia are unlikely to have any symptoms except during an acute exacerbation of the hyponatraemia (4).


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