Ace the 2026 RN Endocrine Exam – Empower Your Nursing Journey!

The hallmark diagnostic test for Syndrome of Inappropriate Antidiuretic Hormone secretion (SIADH) is hypo-osmolality. In SIADH, there is excessive secretion of antidiuretic hormone (ADH), which leads to water retention and dilutional hyponatremia. As water is retained, the osmolality of the blood decreases, resulting in hypo-osmolality. This condition is characterized by low serum osmolality, which, alongside other clinical features, helps in diagnosing SIADH.

In the context of this question, while hypernatremia indicates a deficiency of body water, elevated blood glucose levels and hyperkalemia are not directly related to the mechanisms or characteristics of SIADH. Elevated blood glucose generally pertains to metabolic conditions like diabetes, and hyperkalemia indicates elevated potassium levels often associated with renal dysfunction or adrenal disorders, none of which are typical findings in SIADH. Therefore, understanding that hypo-osmolality is a key diagnostic feature underscores its relevance in the context of SIADH.