ADH :labtest

Why Get Tested?
To help detect, diagnose, and determine the cause of antidiuretic hormone (ADH) deficiency or excess; to investigate low blood sodium levels (hyponatremia); to distinguish between the two types of diabetes insipidus
When to Get Tested?
When you have hyponatremia or have persistent thirst, frequent urination, and dehydration
Sample Required?
A blood sample drawn from a vein in your arm

How is it used?
The antidiuretic hormone (ADH) test is ordered by itself or along with or following other tests 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.
Symptoms of ADH deficiency are 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; nephrogenic diabetes insipidus is characterized by a decrease in the kidney's response to ADH. 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 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.

Symptoms of increased levels of ADH are often seen with "Syndromes of Inappropriate ADH production" or SIADH. Testing for SIADH may include blood and urine osmolality, sodium, potassium, and chloride tests as well as 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 hyponatremia.

Other testing may be performed to help distinguish SIADH from other disorders that can cause edema, hyponatremia, and/or decreased urine production, such as congestive heart failure, liver disease, kidney disease, and thyroid disease.

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