However, there was no associated lowering of urine osmolality. Hyponatremia indicates dilution of sodium in extracellular water, and is almost always evidence of reduction of the concentration of ...

Hyponatremia alone is not a reliable diagnostic ... Serum osmolality, electrolytes, and uric acid, along with urine osmolality and electrolytes, are useful in distinguishing CSW from SIADH.

But excessive water consumption can cause hyponatremia ... which makes urine more concentrated. The reabsorbed water dilutes the blood, bringing osmolality back to normal levels.

SIADH is characterized by decreased serum osmolality with inappropriate urinary ... As a result, sodium excretion in the urine increases, resulting in low serum sodium values (Palmer, 2000).