Hyponatraemia

Causes	Appropriate Tests
	Hyponatraemia may occur with dilution of plasma sodium (total body sodium may be normal or increased) or withdehydration and excess sodium loss. Excessive sodium loss may be renal or extra-renal and the effect may be exacerbated by replacement with oral or IV fluids containing little or no sodium. Electrolytes, urea, creatinine; sodium - urine.
Artefactual result	See Table 1.
	Osmolality; urine - osmolality, sodium.
Dilutional / Water (fluid) overload
Cardiac failure
Cirrhosis
Renal failure
SIADH
Hypothyroidism
Hyperglycaemia
Sodium depletion
Renal sodium loss
Diuretic therapy	Idiosyncratic response.
Salt-wasting renal disease	See Renal tubular disorders
Post-obstructive uropathy	Creatinine, urea; urine - sodium, potassium, osmolality.
Mineralocorticoid deficiency.	See Adrenocortical insufficiency
Extra-renal losses and/or sequestration
Operative blood/fluid loss
Ascites
Sweating, especially Cystic fibrosis
Burn injury	See Burns

Glossary Terms