Antidiuretic Hormone (ADH)
A blood sample drawn from a vein
None needed for an ADH test; however, talk to your healthcare provider about required preparation when the ADH test is performed as part of a water deprivation ADH stimulation test or a water loading ADH suppression test.
Antidiuretic hormone (ADH), also called arginine vasopressin (AVP), is a hormone that helps regulate water balance in the body by controlling the amount of water the kidneys reabsorb while they are filtering wastes out of the blood. This test measures the amount of ADH in the blood.
ADH is produced by the hypothalamus in the brain and stored in the posterior pituitary gland at the base of the brain. ADH is normally released by the pituitary in response to sensors that detect an increase in blood osmolality (number of dissolved particles in the blood) or decrease in blood volume. The kidneys respond to ADH by conserving water and producing urine that is more concentrated. The retained water dilutes the blood, lowers its osmolality, and increases blood volume and pressure. If this is not sufficient to restore the water balance, then thirst is also stimulated so that the affected person will drink more water.
There are a variety of disorders, conditions, and medications that can affect either the amount of ADH released or the kidneys' response to it. ADH deficiency and excess can cause symptoms and complications that, in rare cases, may become life-threatening.
If there is too little ADH or the kidneys do not respond to ADH, then too much water is lost through the kidneys, the urine produced is more dilute, and the blood becomes more concentrated. This can cause excessive thirst, frequent urination, dehydration, and – if you do not drink enough water to replace what is being lost – high blood sodium.
If there is too much ADH, then water is retained, blood volume increases, and the person may experience nausea, headaches, disorientation, lethargy, and low blood sodium.
The ADH test is not widely used to diagnose these conditions. Often, a diagnosis is made on the basis of medical history and other laboratory tests, such as urine and blood osmolality and electrolytes.
ADH deficiency, also called diabetes insipidus, is caused by a lack of ADH or the kidney's inability to respond to ADH.
- Central diabetes insipidus is associated with a lack of ADH production by the hypothalamus or release from the pituitary and may be due to a variety of causes, including an inherited genetic defect, head trauma, a brain tumor, or due to an infection that causes encephalitis or meningitis.
- Nephrogenic diabetes insipidus originates in the kidney and is associated with a lack of response to ADH, causing an inability to concentrate urine. It may be inherited or caused by a variety of kidney diseases.
Both types of diabetes insipidus lead to large volumes of dilute urine eliminated by the kidneys.
Excessive ADH is seen in "syndrome of inappropriate antidiuretic hormone" (SIADH) when ADH is released in unregulated quantities. SIADH is caused by inappropriate production of too much ADH, resulting in water retention, low blood sodium, and decreased blood osmolality.
- The increased production is not due to the normal response to high blood osmolality or low blood volume.
- SIADH may be due to a wide number of diseases and conditions that either stimulate excessive ADH production and release or that prevent its suppression.
- SIADH may also be seen with cancers that produce ADH or ADH-like substances independent of the hypothalamus and pituitary glands.
Regardless of the cause or source, excess ADH causes low blood sodium and osmolality because water is retained and blood volume is increased.
How is the test used?
The antidiuretic hormone (ADH) test may be used to help detect, diagnose, and determine the cause of antidiuretic hormone deficiency or excess. However, this test is not widely used; diagnoses of these conditions are often based on clinical history and other laboratory tests, such as blood and urine osmolality as well as electrolytes.
ADH testing may be done to help diagnose diabetes insipidus and to distinguish between the two main types, central diabetes insipidus and nephrogenic diabetes insipidus, or testing may be done to help diagnose syndrome of inappropriate antidiuretic hormone (SIADH).
When is it ordered?
An ADH test may be ordered by itself, along with other tests, or as part of a water deprivation or water loading procedure when excess or deficient ADH is suspected. It may be ordered when a person has low blood sodium without an identifiable cause and/or has symptoms associated with SIADH. If SIADH develops gradually, there may be no symptoms, but if the condition is acute, the signs and symptoms are usually those associated with water intoxication and may include:
- Nausea, vomiting
- In severe cases, coma and convulsions
An ADH test may be ordered when a person has excessive thirst and frequent urination and the health practitioner suspects diabetes insipidus.
What does the test result mean?
ADH test results alone are not diagnostic of a specific condition. The results are usually evaluated in conjunction with a person's medical history, physical examination, and results of other tests. Low or high levels of ADH may be temporary or persistent, acute or chronic, and may be due to an underlying disease, an infection, an inherited condition, or due to brain surgery or trauma.
In distinguishing between the two types of diabetes insipidus:
- A low ADH may be seen with central diabetes insipidus.
- An increased ADH may be seen with nephrogenic diabetes insipidus.
A water deprivation ADH stimulation test is sometimes used to help distinguish between these types. (For more details, see below.)
An increased level of ADH is often seen with syndromes of inappropriate ADH secretion (SIADH). Testing for SIADH may include blood and urine osmolality, sodium, potassium, and chloride tests, and sometimes an ADH measurement. A water loading ADH suppression test is sometimes performed. (For more details, see below.)
Other testing may be performed to help distinguish SIADH from other disorders that can cause fluid accumulation (edema), low blood sodium, and/or decreased urine production, such as congestive heart failure, liver disease, kidney disease, and thyroid disease.
Increased ADH may also be seen with dehydration, trauma, and surgery. Moderate increases in ADH may be seen with nervous system disorders such as Guillain-Barré syndrome, multiple sclerosis, epilepsy, and acute intermittent porphyria, with pulmonary disorders such as cystic fibrosis, emphysema, and tuberculosis, and in those with HIV/AIDS. The ADH test may sometimes be ordered to help investigate low blood sodium and its associated symptoms, and to identify SIADH, but it is not generally ordered to diagnose or monitor any of the diseases or conditions that may cause it.
In addition to central diabetes insipidus, a low ADH may be seen with drinking large volumes of water, and with low serum osmolality.
What is a water deprivation ADH stimulation test?
A water deprivation ADH stimulation test is sometimes used to confirm a diagnosis of diabetes insipidus and to distinguish between the two types. Under medical supervision, you will be instructed to stop drinking fluids for a specified time. An ADH blood test may be done and you may be given a dose of synthetic ADH. Several blood and urine osmolality measurements are performed at timed intervals before and after vasopressin is given in order to monitor your response to fluid restriction and then to the drug. This procedure must be performed under close medical supervision as it can sometimes lead to severe dehydration and can pose a risk to some people with underlying diseases.
- Central diabetes insipidus is caused by abnormally low production of ADH and the inability to concentrate urine that is reflected as an increase in urine osmolality after ADH administration but not an increase due to water deprivation alone.
- Nephrogenic diabetes insipidus is the kidney's inability to respond to ADH that is reflected as no change in urine osmolality before or after ADH administration and high blood ADH.
What is a water loading ADH suppression test?
A water loading ADH suppression test may be used to help diagnose SIADH. With this procedure, you will be instructed to fast and then will be given specific quantities of water to drink. The amount of urine produced and the changes in urine and blood osmolality are monitored over time. An ADH blood test is also performed. This procedure must be performed under medical supervision as it can be risky in people with kidney disease and could result in severe low blood sodium.
With this test, people with SIADH typically have decreased blood sodium and osmolality. They do not produce as much urine as expected, urine osmolality is high relative to serum osmolality, and the ADH concentration is in excess of what would be appropriate and does not decrease appropriately with water loading.
Is there anything else I should know?
In general, the ability to concentrate urine decreases with age.
ADH production temporarily increases when a person is standing, during the night, and with pain, stress and exercise. Production decreases with hypertension and when someone is lying down.
Are there medications that can affect ADH levels?
Many medications can affect ADH levels. They include:
- Drugs that stimulate ADH release, such as: barbiturates, desipramine, morphine, nicotine, amitriptyline and carbamazepine.
- Drugs that promote ADH action, such as: acetaminophen, metformin, tolbutamide, aspirin, theophylline, and non-steroidal anti-inflammatory drugs.
- Drugs that decrease ADH or its effects, such as: ethanol, lithium, and phenytoin.
How is diabetes insipidus different than diabetes mellitus?
Diabetes mellitus, usually referred to as diabetes, is related to either decreased insulin production or insulin resistance and causes an increase in blood glucose. Diabetes insipidus is not related to insulin or glucose. The ancient Greeks, in naming the diseases, thought that both conditions were similar because persons with them had increased thirst and frequent urination. They were different in that, in one, the urine was sweet (diabetes mellitus) while in the other, it was tasteless (diabetes insipidus).
Can diabetes insipidus be treated?
Yes, a synthetic form of ADH can be given as a replacement to people with central diabetes insipidus. Individuals with nephrogenic diabetes insipidus are encouraged to drink adequate amounts of water to replace what is being lost in their urine and should talk to their healthcare provider about possible adjustments to their diet. For additional details, see the links under Related Content.