diagnosis of SIADH
Last reviewed 04/2022
The following criteria should be fulfilled for a diagnosis of SIADH to be made:
- plasma sodium concentration <135 mmol/l
- plasma osmolality <280 mOsmol/kg
- urine osmolality > 100 mOsmol/kg
- urinary sodium concentration >30mmol/L
- patient clinically euvolaemic
- absence of clinical or biochemical features of adrenal and thyroid dysfunction.
- no diuretic use (recent or past) (1,2)
The following investigations could be carried out in SIADH
- urea and electrolytes
- plasma and urine osmolality
- urinary sodium
- thyroid function tests
- a short synacthen test (1)
- chest and skull radiographs may be useful in excluding other causes of SIADH.
- it is important to exclude diuretic use (especially thiazides), hypothyroidism and adrenal insufficiency before the diagnosis of SIADH is made (3)
- (1) Thompson CJ, Crowley RK. Hyponatraemia. J R Coll Physicians Edinb2009; 39:154–7
- (2) Hannon MJ, Thompson CJ. The syndrome of inappropriate antidiuretic hormone: prevalence, causes and consequences. Eur J Endocrinol. 2010;162 Suppl 1:S5-12
- (3) Hoorn EJ, van der Lubbe N, Zietse R. SIADH and hyponatraemia: why does it matter?NDT Plus. 2009;2(Suppl_3):iii5-iii11.