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Hypoosmolar hyponatremia is a condition where hyponatremia is associated with a low plasma osmolality. [1] The term "hypotonic hyponatremia" is also sometimes used.[2]When the plasma osmolarity is low, the extracellular fluid volume status may be in one of three states: low volume, normal volume, or high volume.
A low serum osmolality will suppress the release of ADH, resulting in decreased water reabsorption and more concentrated plasma. Syndrome of inappropriate ADH secretion occurs when excessive release of antidiuretic hormone results in inappropriately elevated urine osmolality (>100 mOsmol/L) relative to the blood plasma, leading to hyponatraemia.
Diagnosis is based on clinical and laboratory findings of low serum osmolality and low serum sodium. [13] Urinalysis reveals a highly concentrated urine with a high fractional excretion of sodium (high sodium urine content compared to the serum sodium). [14] A suspected diagnosis is based on a serum sodium under 138.
The causes of and treatments for hyponatremia can only be understood by having a grasp of the size of the body fluid compartments and subcompartments and their regulation; how under normal circumstances the body is able to maintain the sodium concentration within a narrow range (homeostasis of body fluid osmolality); conditions can cause that ...
Similarly, it is said to be hypoossmolar if the osmolarity, or osmatic concentration, is too low. For example, if the osmolarity of parenteral nutrition is too high, it can cause severe tissue damage. [7] One example of a condition caused by hypoosmolarity is water intoxication. [8]
The calculated osmolality is then subtracted from the measured osmolality to provide the osmol gap, or the difference between these two values. If this gap falls within an acceptable range,(<10) then it is assumed that sodium, glucose, BUN are indeed the major dissolved ions and molecules in the serum.
A relative insulin deficiency leads to a serum glucose that is usually higher than 33 mmol/L (600 mg/dL), and a resulting serum osmolarity that is greater than 320 mOsm. This leads to excessive urination (more specifically an osmotic diuresis ), which, in turn, leads to volume depletion and hemoconcentration that causes a further increase in ...
Central diabetes insipidus can be caused by various congenital or acquired lesions, and when the cause is unknown, it is classified as idiopathic. The water deprivation test (WDT) is a commonly used test for diabetes insipidus , a two-step process involving parenteral desmopressin administration after an initial 8-hour water fast.