When caring for a patient with syndrome of inappropriate antidiuretic hormone (SIADH), which laboratory value is expected?

In the context of syndrome of inappropriate antidiuretic hormone (SIADH), a key laboratory value to anticipate is hyponatremia, which refers to a low sodium concentration in the blood. SIADH is characterized by excessive secretion of antidiuretic hormone (ADH) despite normal or low plasma osmolality. This leads to water retention, dilution of sodium, and ultimately, a decrease in serum sodium levels.

The expected laboratory value in a patient with SIADH is typically a sodium level significantly lower than the normal range of approximately 135-145 mEq/L. A sodium level of 128 mEq/L is indicative of hyponatremia, which aligns with the physiological disturbance caused by SIADH. This dilutional hyponatremia can lead to various symptoms, including headache, changes in mental status, and potentially severe neurological complications if not managed.

In this case, the other sodium values represent normal or slightly elevated levels, which would not be consistent with the hyponatremia that characterizes SIADH. Thus, the expected laboratory value for a patient with SIADH is indeed a sodium level of 128 mEq/L, confirming the diagnosis and emphasizing the need for careful monitoring