SIADH

Syndrome of inappropriate antidiuretic hormone secretion: characterised by hyponatraemia, with urine sodium >20 mmol/L and urine osmolality > plasma osmolality.

Osmolality - plasma and urine; sodium - plasma and urine; levels of creatinine, urea and urate tend to be low in SIADH but high in patients in whom hyponatraemia is associated with hypovolaemia.

Hypothyroidism, Addison’s disease and diuretic therapy must be excluded on clinical or pathological findings.