Are there circumstances in which you would check a serum copeptin level when evaluating patients for possible SIADH?  

I would check a serum copeptin level in a patient suspected of having nephrogenic syndrome of inappropriate antidiuresis (nephrogenic SIAD). Since the vasopressin 2 receptor is constitutively activated, these patients present with hyponatremia, low serum osmolality, high urinary sodium, and ele...