clinical features

Last reviewed 04/2022

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).