21st May 2025

Causes of Hyponatraemia

Hypovolaemia	Euvolaemia	Hypernatraemia
Renal loss (Diuretics, Osmotic diuresis, mineralocorticoid deficiency i.e. Addison’s disease, pituitary failure or hypothalamic failure, salt wasting nephropathies) Extra renal loss (diarrhoea/ vomiting) Fluid losses via 3rd spacing, bowel obstruction) Cerebral salt wasting syndrome (diagnosis of exclusion)	SIADH Hypothyroidism Adrenal insufficiency Stress Drugs (ecstasy use)	Congestive cardiac failure Cirrhosis/ hepatic failure Nephrotic syndrome/ hypoalbuminaemia

Table 1: Causes of Hyponatraemia

Pulmonary embolism is also a common cause of hyponatraemia within hospital in-patients.

Drug	Class	Mode of action
Bendroflumethiazide	Thiazide diuretic	Inhibits sodium reabsorption in distal convoluted tubule
Indapamide	Thiazide-like diuretic	Inhibits sodium reabsorption in distal convoluted tubule
Furosemide	Loop diuretic	Inhibits sodium and chloride reabsorption in the ascending loop of Henle
Citalopram	Selective serotonin re-uptake inhibitor	Not fully understood
Haloperidol	Anti-psychotic	Not fully understood
Carbamazepine	Anti-epileptic	Not fully understood
Other drug causes of hyponatraemia	MDMA (ecstasy), opioids, ACEi, ARBs, PPIs, anticonvulsants, amiodarone, theophylline, dopamine agonists (metoclopramide, domperidone), insulin, NSAIDs

Table 2: Drug-related causes of hyponatraemia

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