Isotonic hyponatremia Isotonic hyponatremia Isotonic hyponatremia is a form of hyponatremia with mOsm measured between 280 and 295. It can be associated with pseudohyponatremia, or with isotonic infusion of glucose or mannitol. Certain conditions, such as extraordinarily high blood levels of lipid (hyperlipidemia/hypertriglyceridemia) or protein (hyperparaproteinemia), magnify the electrolyte exclusion effect. This interferes with the measurement of serum sodium concentration by certain methods, leading to an erroneously low "measurement" of sodium, or pseudohyponatremia. The methods affected are the flame-photometric and indirect (but not direct) ion-selective electrode assays. This is distinct from a true dilutional hyponatremia that can be caused by an osmotic
Hypotonic hyponatremia blood volume that is no longer there, that has been lost from the body. As a result, their blood volume is reduced. As mentioned above, lack of adequate blood volume is a potent stimulus for ADH secretion and thence water retention. Some patients with hyponatremia have normal or slightly elevated blood volume. In those patients, the increased ADH activity and subsequent water retention may be due to "physiologic" causes of ADH release such as pain or nausea. Alternatively, they may have the Syndrome of Inappropriate ADH (SIADH). SIADH represents the sustained, non-physiologic release of ADH and most often occurs as