Hyponatraemia

Severity

Range

Mild
Na 130–134
Moderate
Na 125–129
Severe
Na < 125 or symptomatic

🏜️

Hypovolaemic Causes

Vomiting, diarrhoea, NG lossesHigh-output stoma / fistulaPancreatitis / third-spacingThiazide & loop diureticsSalt-wasting nephropathyAddison's / cortisol deficiency

🧠

Euvolaemic (SIADH) Causes

Stroke, head injury, SAH, meningitisPituitary surgerySmall-cell lung cancer / brain tumourPneumonia (esp. Legionella), TB, COPDSSRIs, TCAs, carbamazepine, antipsychotics, PPIs, opioids, MDMA, desmopressinHypothyroidism

❤️

Hypervolaemic (overloaded) Causes

Congestive cardiac failureCirrhosis with ascitesNephrotic syndromeAdvanced CKD / AKIConstrictive pericarditis

🧪

Spurious Causes

Pseudohyponatraemia (hyperlipidaemia, paraproteins)Hyperglycaemia (translocational)Primary polydipsia / beer potomania / tea-and-toast