Diagnosis is based on clinical and laboratory findings of low serum osmolality and low serum sodium. Urinalysis reveals a highly concentrated urine with a high fractional excretion of sodium (high sodium urine content compared to the serum sodium). A suspected diagnosis is based on a serum sodium under 138. A confirmed diagnosis has seven elements: 1) a decreased effective serum osmolality - 1%; 7) a fractional urea excretion >55%; 8) an abnormal water load test; and 9) an elevated plasma AVP. Differential diagnosis<unk><unk>  (ADH) is released from the posterior pituitary for a number of physiologic reasons. The majority of people with hyponatremia, other than those with excessive water intake (polydipsia) or renal salt wasting, will have elevated ADH as the cause of their hyponatremia. However, not every person with hyponatremia and elevated ADH has<unk> . One approach to a diagnosis is to divide ADH release into appropriate (not<unk>  or<unk> <unk> . Appropriate ADH release can be a result of hypovolemia, a so-called non-osmotic trigger of ADH release. This may be true hypovolemia, as a result of dehydration with fluid losses replaced by free water. It can also be perceived hypovolemia, as in the conditions of congestive heart failure (CHF) and cirrhosis in which the kidneys perceive a lack of intravascular volume. The hyponatremia caused by appropriate ADH release (from the kidneys' perspective) in both CHF and cirrhosis have been shown to be an independent poor prognostic indicator of mortality. Appropriate ADH release can also be a result of non-osmotic triggers. Symptoms such as nausea/vomiting and pain are significant causes of ADH release. The combination of osmotic and non-osmotic triggers of ADH release can adequately explain the hyponatremia in the majority of people who are hospitalized with acute illness and are found to have mild to moderate hyponatremia.<unk>  is less common than appropriate release of ADH. While it should be considered in a differential, other causes should be considered as well. Cerebral salt wasting syndrome (CSWS) also presents with hyponatremia, there are signs of dehydration for which reason the management is diametrically opposed to<unk> . Importantly CSWS can be associated with subarachnoid hemorrhage (SAH) which may require fluid supplementation rather than restriction to prevent brain damage. Most cases of hyponatremia in children are caused by appropriate<unk>  of<unk><unk>  rather than<unk>  or another cause.
Syndrome of inappropriate antidiuretic hormone secretion
Central diabetes insipidus
Nephrogenic diabetes insipidus
Apparent mineralocorticoid excess syndrome
Primary polydipsia
Adrenal crisis
Cerebral salt-wasting syndrome
Exercise-associated hyponatremia