• Blood sample contaminated with sodium citrate or pseudohypernatraemia

Hypovolaemic hypernatraemia

• Poor water intake (may be seen in advanced dementia, with diminished thirst)
• Osmotic diuretics
• Vomiting
• Diarrhoea
• Fistulas
• Major burns
• Hyperosmolar hyperglycaemic state (HHS)

Euvolaemic hypernatraemia

• Increased insensible water loss, for example hyperventilation
• Osmotic diuresis such as glycosuria
• Diabetes insipidus (cranial or nephrogenic causes)

Hypervolaemic hypernatraemia

• Excessive sodium intake, for example hypertonic saline, or drugs containing sodium such as carbenicillin or sodium bicarbonate, salt poisoning
• Mineralocorticoid excess, for example Conn's syndrome or Cushing's syndrome