Typical exam stem
A patient is found to have serum sodium of 118 mmol/L. Explain how you would determine the cause and decide whether urgent treatment is required.
Active exam mode
Plan the case before reading, then mark sections, reveal pearls and self-rate the viva.
1. Sixty-second answer plan
1:00Before reading the notes, say or write your assessment, investigations and management structure.
2. Section checklist
Mark each section only after you can explain its main decision points without reading.
3. Exam-pearl flashcards
Try to predict the pearl before revealing it.
4. Viva drill
Answer aloud before rating yourself. Anything marked “review” stays visible in your progress.
How do you distinguish hypotonic from non-hypotonic hyponatraemia?
Progress is saved on this device. Use “Reset session” when you want a fresh attempt.
First decide whether the sodium is causing an emergency
Severity of symptoms matters as much as the absolute sodium value. Seizures, reduced consciousness, severe confusion or signs of cerebral oedema suggest a neurological emergency and justify urgent controlled correction in a monitored setting.
If symptoms are not severe, there is usually time to establish the physiology before treatment.
A reproducible diagnostic sequence
- Confirm true hyponatraemia and assess serum osmolality to distinguish hypotonic from non-hypotonic states.
- In hypotonic hyponatraemia, assess urine osmolality to determine whether water excretion is appropriately suppressed.
- Use urine sodium together with clinical volume assessment to separate likely hypovolaemic, euvolaemic and hypervolaemic causes.
- Review diuretics, renal disease, heart failure, cirrhosis, vomiting, adrenal insufficiency, hypothyroidism and excessive water intake.
- Do not diagnose SIADH until important alternative causes, especially adrenal insufficiency and relevant medication effects, have been excluded.
Treatment principle
Treat severe symptomatic hyponatraemia with carefully monitored hypertonic saline according to a validated protocol. Once immediate neurological danger is controlled, treatment becomes cause-specific. Chronic hyponatraemia must not be corrected too rapidly because osmotic demyelination can follow over-correction.
Serial sodium measurement is essential whenever active correction is underway. Patients at high risk of osmotic demyelination require particularly conservative correction limits and expert input.
Guideline source for further reading
This page is an original exam-revision summary. For clinical decisions, use current local protocols and the primary guidance below.