Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)
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Updated 18 Oct 2021
Hyponatraemia, an electrolyte imbalance characterised by low salt concentration in the body, has the potential to cause serious complications including death (Tee & Dang 2017).
Despite this, syndrome of inappropriate antidiuretic hormone secretion (SIADH), which is one of the most common causes of hyponatraemia, is often underdiagnosed and undermanaged (Tee & Dang 2017).
What is Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)?
Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a condition where the body creates excessive amounts of the antidiuretic hormone (ADH) (also called vasopressin) (Tauro 2020).
ADH, which is responsible for regulating the level of water in the body, is created in the hypothalamus in the brain and secreted by the pituitary gland. ADH helps the kidneys retain the correct amount of water and is therefore responsible for how much water is conserved and eliminated through urination (MedlinePlus 2021; Radhakrishnan & Allarakha 2021).
In SIADH, the secretion of ADH is unable to be suppressed. This causes an impaired ability to excrete water through urine output, which disturbs the body’s salt balance and results in the development of hyponatraemia (Tauro 2020; Sterns, Emmett & Forman 2021).
The resulting hyponatraemia can be acute (developing within 48 hours) or chronic (developing over days or weeks). Acute hyponatraemia is much more dangerous as it develops so rapidly the brain cells don’t have enough time to properly adjust (MedlinePlus 2021).
In many cases, SIADH is reversible (MedlinePlus 2021).
Causes of SIADH
There are a variety of potential causes for SIADH, including:
Mild SIADH is often asymptomatic, however, the more the body’s salt concentration decreases, the more severe symptoms become. Patients might experience:
In older adults with mild SIADH, some symptoms such as confusion might be misattributed to age (Tauro 2020).
In severe cases, the hyponatraemia caused by SIADH can lead to coma, brain herniation or death (MedlinePlus 2021).
Diagnosis of SIADH
SIADH is diagnosed by taking urine and blood tests to detect the levels of sodium and potassium in the body and measure osmolality (the concentration of these electrolytes in the blood and urine) (CHOP 2014).
The criteria for diagnosis of SIADH is as follows:
Decreased serum osmolality (<275 mOsm/kg)
Increased urine osmolality (>100 mOsm/kg)
Euvolaemia (normal blood fluid volume)
Increased sodium in urine (>20 mmol/L)
No other identified cause of hyponatraemia (e.g. diuretic use, hypothyroidism, cortisol deficiency, marked hyperproteinaemia, hyperlipidaemia or hyperglycaemia).
(Tee & Dang 2017)
Treatment of SIADH
There are several potential treatments for SIADH, including:
Addressing underlying causes (e.g. adjusting or changing a medicine that is contributing to the issue)
High-salt infusion to treat acute cases
Fluid restriction (limiting the amount of water consumed)
Taking certain medicines that encourage the elimination of the excess fluid
Taking certain medicines that limit the production of ADH.
(Tauro 2020)
The specific treatment used will depend on:
The patient’s age, health and medical history
The extent of the condition
The patient’s tolerance to medicines, procedures and therapies
MedlinePlus 2021, Syndrome of Inappropriate Antidiuretic Hormone Secretion, U.S. Department of Health and Human Services, viewed 1 October 2021, https://medlineplus.gov/ency/article/000314.htm
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