After surgical clipping of a cerebral aneurysm, a client develops SIADH. Which manifestation is most consistent with excessive ADH?

• A. Polyuria
• B. Weight gain
• C. Hyponatremia
• D. Decreased specific gravity

Answer: (C)

Excess ADH causes the kidneys to reabsorb more free water, expanding total body water without adding salt. This dilutes the blood sodium concentration, producing hyponatremia. Hyponatremia is the key finding in SIADH and can lead to neurologic symptoms as sodium falls.

While fluid retention can cause weight gain, the hallmark manifestation tied to SIADH is the low serum sodium. The urine in SIADH becomes concentrated because water is being reabsorbed, so urine specific gravity is high rather than decreased. Polyuria would be unlikely since ADH promotes water conservation, not excessive urination.