Hyponatraemia
Hyponatraemia may be caused by water excess or sodium depletion. Causes of pseudohyponatraemia include hyperlipidaemia (increase in serum volume) or a taking blood from a drip arm. Urinary sodium and osmolarity levels aid making a diagnosis
Sodium depletion, renal loss (patient often hypovolaemic)
Patient often euvolaemic
Urinary sodium < 20 mmol/l
Sodium depletion, extra-renal loss
Water excess (patient often hypervolaemic and oedematous)
Urinary sodium > 20 mmol/l
Sodium depletion, renal loss (patient often hypovolaemic)
- diuretics
- Addison's
- diuretic stage of renal failure
Patient often euvolaemic
- SIADH (urine osmolality > 500 mmol/kg)
- hypothyroidism
Urinary sodium < 20 mmol/l
Sodium depletion, extra-renal loss
- diarrhoea, vomiting, sweating
- burns, adenoma of rectum
Water excess (patient often hypervolaemic and oedematous)
- secondary hyperaldosteronism: heart failure, cirrhosis
- reduced GFR: renal failure
- IV dextrose, psychogenic polydipsia