Hyponatraemia

Causes

Appropriate Tests

 

Hyponatraemia may occur with dilution of plasma sodium (total body sodium may be normal or increased) or with dehydration 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 minimal or no sodium.

Electrolytes, Urea, Creatinine, Sodium urine.

Artefactual result

See Table 1.

 

Osmolality, Osmolality urine, 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; Sodium urine, 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.