Antidiuretic Hormone (ADH)

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).

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:

• Headache
• Nausea, vomiting
• Confusion
• 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.

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.

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.)

SIADH may be due to a variety of cancers, including leukemia, lymphoma, and cancers of the lung, pancreas, bladder, and brain. Levels of ADH may be greatly increased with such cancers.

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.

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.

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.

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.

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.

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).

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.