This is one of the most common causes of hyponatraemia; patients produce an inappropriately concentrated urine when there is no discernible stimulus for release of antidiuretic hormone (1).
The following criteria should be fulfilled before a diagnosis of SIADH can be made:
- persistent excretion of concentrated urine with no reason for ADH release
- normal renal and adrenal function
- no oedema or hypovolaemia should be present