Table 3

Causes of hyponatraemia19–21

Sodium loss (hypovolaemic hyponatraemia)Normovolemic hyponatremiaWater excess (hypervolaemic hyponatraemia)
Skin
  • Severe sweating

  • Cystic fibrosis

  • Burns

Abnormal ADH release
  • Vagal neuropathy (failure of inhibition of ADH release)

  • Deficiency of ACTH or glucocorticoids (Addison's disease)

  • Hypothyroidism

  • Severe potassium depletion

Hypoalbuminaemia
  • Nephrotic syndrome

  • Liver disease/failure

Gut
  • Vomiting

  • Diarrhoea (laxative abuse)

  • Peritonitis

  • Drains/fistula

  • Haemorrhage

SIADH
  • Cerebral disease (meningitis + other infections + CNS trauma)

  • Respiratory illness (pneumonia + tumours)

  • Intermittent positive-pressure ventilation

  • Drugs, eg, carbamazepine, barbiturates

  • Pain/trauma

  • Nausea/vomiting

Fluid overload
  • Congestive heart failure

  • Acute and chronic renal failure – oliguria

  • Iatrogenic fluid hydration

  • Psychogenic polydipsia

Kidney
  • Osmotic diuresis (eg, hyperglycaemia-DKA)

  • Adrenocortical insufficiency

  • Adrenocortical resistance

  • Pseudohypoaldosteronism

  • Cerebral salt-wasting syndrome

  • Tubulo-intestinal renal disease

  • Unilateral renal artery stenosis

  • Recovery phase of acute tubular necrosis

  • Diuretic abuse/iatrogenic

ADH-like substance
  • Oxytocin

  • DDAVP

Unmeasured osmotically active substances stimulating osmotic ADH release
  • Glucose

  • Alcohol

  • Mannitol

  • Sick cell syndrome (leakage of intracellular ions)

  • ACTH, adrenocorticotrophic hormone; ADH, antidiuretic hormone; DDAVP, 1-deamino-D-arginine vasopressin; DKA, diabetic ketoacidosis; SIADH, syndrome of inappropriate ADH secretion.