In a patient with SIADH, what would you expect to find regarding urine osmolality?

In the context of Syndrome of Inappropriate Antidiuretic Hormone secretion (SIADH), it is expected that urine osmolality would be higher than plasma osmolality. This condition is characterized by excessive release of antidiuretic hormone (ADH), which leads to increased reabsorption of water in the kidneys. As a result, the kidneys retain more water, causing dilution of plasma solutes and decreasing plasma osmolality.

In SIADH, despite low plasma osmolality, the kidneys continue to concentrate the urine due to the elevated levels of ADH. Therefore, urine osmolality is often significantly elevated, which can exceed plasma osmolality. This is a distinguishing feature of SIADH, as adequate hydration would typically lead to dilutional effects on urine concentration, but the inappropriate secretion of ADH overrides this natural response. Thus, in a patient with SIADH, one would expect the urine osmolality to be higher than that of the plasma, confirming the diagnosis.