A nurse is providing care for a client who has syndrome of inappropriate antidiuretic hormone (SIADH). Which of the following physiological alterations is consistent with a diagnosis of SIADH?

A. Increased serum sodium: SIADH is characterized by excessive secretion of antidiuretic hormone (ADH), which leads to increased water reabsorption by the kidneys. This excess water dilutes the blood, resulting in hyponatremia. B. Decreased serum osmolality: SIADH causes excessive water retention, leading to dilution of the blood and decreased serum osmolality. This is a hallmark of SIADH, as the body's water balance is disturbed. C. Decreased urine osmolality: In SIADH, urine osmolality is typically high due to concentrated urine caused by the kidneys retaining water. This is in contrast to a low osmolality seen in other conditions like diabetes insipidus. D. Decreased urinary sodium: In SIADH, urinary sodium levels are often elevated as the kidneys try to excrete excess water, but they still retain sodium due to the influence of antidiuretic hormone (ADH).