A patient is admitted with possible syndrome of inappropriate anti-diuretic hormone (SIADH). Which information obtained by the nurse is most important to communicate rapidly to the health care provider?

A. Urine specific gravity of 1.025: This value indicates concentrated urine but is only moderately elevated and not immediately life-threatening. While it supports the diagnosis of SIADH, it does not require rapid intervention compared with critically low sodium. B. Severe headache: Headache is a common symptom of hyponatremia due to cerebral edema. Although it indicates neurologic involvement, it is a nonspecific symptom and does not quantify the severity of the underlying electrolyte disturbance. C. Extreme thirst: Thirst is a compensatory mechanism for low serum osmolality, but in SIADH, fluid restriction is indicated. While it is a notable symptom, it does not represent an immediate danger compared with critically low sodium. D. Serum sodium level of 119 mEq/L: Hyponatremia below 120 mEq/L is severe and can rapidly lead to cerebral edema, seizures, and potentially life-threatening neurologic complications. Prompt communication with the healthcare provider is essential to initiate interventions such as hypertonic saline, fluid restriction, or medications to correct sodium safely.