How is SIADH Diagnosed?

The key to the diagnosis of SIADH is to distinguish it from other causes of dilutional hyponatraemia. The most common causes of a dilutional hyponatraemia are excess infusion of dextrose/saline drips and diuretic administration.

The diagnosis is confirmed by demonstrating the following:

• Hyponatraemia (serum sodium less than 130mmol/L)
• Plasma hypo-osmolality
• Elevated urine osmolality
• The exclusion of adrenal, renal and thyroid dysfunction.