Hyponatraemia
Hyponatraemia means blood sodium is below the reference range, usually because water balance is abnormal rather than because the diet lacks salt. A rapid or severe fall can cause brain swelling, confusion and seizures.
Key takeaways
- The sodium result, speed of change, symptoms and fluid status determine urgency and treatment.
- Diuretics, SIADH, heart or liver disease, kidney problems and excessive water intake require different approaches.
- Correcting chronic hyponatraemia too quickly can cause permanent neurological injury.
A sodium-related medicine listing cannot identify the cause or safe correction rate; blood and urine tests plus monitored clinical assessment are required.
How is the cause investigated?
Clinicians confirm glucose and blood osmolality, assess volume status and review medicines. Urine sodium and osmolality help distinguish water retention from sodium loss. Adrenal and thyroid disorders may also need exclusion.
How does treatment differ by cause?
Treatment may involve restricting fluid, replacing volume, stopping a contributing medicine or treating heart, liver, adrenal or thyroid disease. Tolvaptan promotes water excretion in selected cases but needs close sodium and liver monitoring; it is not a general correction medicine. See hormone therapy for class context.
When to seek urgent care
Seek emergency care for new confusion, seizure, inability to wake normally, severe headache with vomiting, collapse or rapidly worsening neurological symptoms. Do not attempt correction by taking salt or restricting water without advice.