Hyponatraemia: common and commonly misunderstood

Pat Phillips



Hyponatraemia is common and has many causes. Although often asymptomatic or associated with nonspecific symptoms, diagnosis and treatment are required as it can lead to cerebral problems if it becomes severe.

Key Points

  • Hyponatraemia is common in patients with myocardial dysfunction or chronic conditions such as hypertension, type 2 diabetes and obesity.
  • Plasma sodium levels may be misleading because of laboratory errors, solute excess or the presence of substances that are not soluble in water.
  • Generally, chronic hyponatraemia is asymptomatic or associated with nonspecific symptoms such as tiredness and cramps. Acute or severe hyponatraemia, however, may be associated with impaired consciousness, seizures and death.
  • Investigations include repeating the sodium measurement, excluding spurious hyponatraemia and measuring urine electrolytes. Further investigations may be needed to define the underlying causes of water excess (either ‘appropriate’ or ‘inappropriate’ secretion of antidiuretic hormone) or sodium depletion (usually excess sodium loss).
  • Management aims to correct any underlying clinical cause and to correct the hyponatraemia by increasing the urinary cation excretion (by increasing sodium and potassium intake), diluting the urine (by using loop diuretics) and maintaining or increasing urine output.
  • More active intervention such as intravenous hypertonic saline and/or vasopressin agonists may be needed in patients with acute severe hyponatraemia; these patients should be closely monitored in an intensive care environment.