Hyponatremia

Hyponatremia is an electrolyte disorder in which blood sodium falls below normal, so that water moves into cells and makes them swell. The brain is especially sensitive to this swelling. It is more often a problem of too much body water than of too little dietary sodium. Causes include heart failure, cirrhosis, kidney disease, severe vomiting or diarrhoea, excessive fluid intake, diuretic medicines, some antidepressants and the syndrome of inappropriate antidiuretic hormone secretion. Mild cases may cause no symptoms; headache, nausea, cramps, fatigue and confusion can occur, and severe cases risk seizures, coma and brain herniation. Blood tests measuring sodium, supported by urine tests and osmolality, confirm it. Treatment targets the underlying cause and may involve fluid restriction, intravenous fluids, adjusting medicines, or an aquaretic such as tolvaptan.

Seek urgent care for unusual bleeding or bruising, breathlessness at rest, or a swollen painful leg. See a doctor for persistent tiredness, pale skin, or any symptom of anaemia in a man or a woman after the menopause, which always needs a cause to be found. Call the local emergency number for any symptom that is sudden and severe. This page is a reference for healthcare professionals and does not replace an assessment.