Table 2

 Overview of the causes of hyponatraemia in primary care and guide to suggested action levels*

Hyponatraemia: causes5,8
*Thresholds for referral should, however, be based principally on clinical state and rate of change.
†Such as: antidepressants, e.g. tricyclics, selective serotonin reuptake inhibitors; antidiabetic drugs, e.g. chlorpropramide, metformin; antineoplastic agents, e.g. vinca alkaloids, cyclophosphamide, cisplatin; antipsychotic drugs, e.g. phenothiazines, butyrophenones; analgesics, e.g. non-steroidal anti-inflammatory drugs; antiepileptic drugs, e.g. carbamazepine, sodium valproate; diuretics, e.g. thiazides, amiloride; and other drugs, e.g. alpha interferon, ecstasy.
Pseudohyponatraemia: hyperproteinaemia, hypertriglyceridaemia Osmotic shift: hyperglycaemia
Hypovolaemia (with net sodium depletion)Skin loss: sweating
Gut loss: vomiting, diarrhoea
Renal loss: diuretics, Addison’s disease, hyperglycaemia
Hypervolaemia (with net water retention)Congestive cardiac failure
Cirrhosis with ascites
Nephrotic syndrome or chronic kidney disease
Clinical euvolaemia (due to water retention and sodium loss)SIADH and related syndromes
Malignancy; typically lung, upper gastrointestinal
Chronic lung disease, infection, abscess
Cerebral injury, stroke, infection