The antidiuretic hormone (ADH) test is used to help detect, diagnose, and determine the cause of antidiuretic hormone deficiencies and excesses. 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.
Antidiuretic hormone, also called arginine vasopressin (AVP), is a hormone produced by the hypothalamus in the brain and stored in the posterior pituitary gland at the base of the brain. ADH helps regulate water balance in the body. A variety of disorders, conditions, and medications can affect either the amount of ADH released or the kidneys' response to it.
ADH deficiency is often seen with one of two types of diabetes insipidus. Central diabetes insipidus is a decrease in the production of ADH by the hypothalamus or in the release of ADH from the pituitary while nephrogenic diabetes insipidus is characterized by a decrease in the kidney's response to ADH. Both types of diabetes insipidus lead to the excretion of large quantities of dilute urine.
A water deprivation ADH stimulation test is sometimes used to distinguish between these types. It involves fluid restriction, an ADH test, and the administration of ADH (vasopressin). Several blood and urine osmolality measurements are performed at timed intervals before and after vasopressin is given in order to monitor the body's 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.
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. With this procedure, a fasting person is given specific quantities of water and then the amount of urine produced and the changes in urine and blood osmolality are monitored over time. An ADH test is also performed. This procedure must also be performed under medical supervision as it can be risky in those with kidney disease and can sometimes result in severe low blood sodium (hyponatremia).
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 production and secretion 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:
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. Excesses and deficiencies 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.
With ADH suppression or stimulation tests, a health practitioner is looking for appropriate levels of ADH, osmolality, and kidney water retention responses.
A water loading ADH suppression test may be used to help diagnose SIADH. With this test, those 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.
A water deprivation ADH stimulation test may be used to differentiate between the two types of diabetes insipidus.
Central diabetes insipidus is characterized 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.
This article was last reviewed on March 6, 2014. | This article was last modified on March 6, 2014.
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