Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a condition in which the body makes too much antidiuretic hormone (ADH). This hormone helps the kidneys control the amount of water your body loses through the urine. SIADH causes the body to retain too much water.
ADH is a substance produced naturally in an area of the brain called the hypothalamus. It is then released by the pituitary gland at the base of the brain.
There are many reasons why the body needs to make a lot of ADH. Common situations when ADH is released into the blood when it should not be produced (inappropriate) include:
Rare causes include:
With SIADH, the urine is very concentrated. Not enough water is excreted and there is too much water in the blood. This dilutes many substances in the blood such as sodium. A low blood sodium level is the most common cause of symptoms of too much ADH.
Often, there are no symptoms from a low sodium level.
When symptoms do occur, they may include any of the following:
The health care provider will perform a complete physical examination to help determine the cause of your symptoms.
Lab tests that can confirm and help diagnose low sodium include:
Treatment depends on the cause of the problem. For example, surgery is done to remove a tumor producing ADH. Or, if a medicine is the cause, its dosage may be changed or another medicine may be tried.
In all cases, the first step is to limit fluid intake. This helps prevent excess fluid from building up in the body. Your provider will tell you what your total daily fluid intake should be.
Medicines may be needed to block the effects of ADH on the kidneys so that excess water is excreted by the kidneys. These medicines may be given as pills or as injections given into the veins (intravenous).
Outcome depends on the condition that is causing the problem. Low sodium that occurs rapidly, in less than 48 hours (acute hyponatremia), is more dangerous than low sodium that develops slowly over time. When sodium level falls slowly over days or weeks (chronic hyponatremia), the brain cells have time to adjust and the acute symptoms such as brain swelling don't occur. Chronic hyponatremia is associated with nervous system problems such as poor balance and poor memory. Many causes of SIADH are reversible.
In severe cases, low sodium can lead to:
When your body's sodium level drops too much, it can be a life-threatening emergency. Call your provider right away if you have symptoms of this condition.
Reviewed By: Brent Wisse, MD, board certified in Metabolism/Endocrinology, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.