Hypotonic hyponatremia

Hypoosmolar hyponatremia is a condition where hyponatremia associated with a low plasma osmolality. The term “hypoosmolar hyponatremia” is also sometimes used.

When the plasma osmolality is low, the extracellular fluid volume status may be in one of three states: low volume, normal volume, or high volume.

SIADH: hypotonic hyponatremia (efective serum osmolality <275 mOsm/L) within appropriately high urinary concentration (urine osmol>100 mOsm/L) and euvolemia or hypervolemia.