Dr Leigh Martens

General Practitioner

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Blood-tests Explained


Disclaimer:

This website is intended to assist with patient education and should not be used as a diagnostic, treatment or prescription service, forum or platform. Always consult your own healthcare practitioner for a more personalised and detailed opinion

ADH


At a Glance

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 low blood sodium or have persistent thirst, frequent urination, and dehydration

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None needed for an ADH test; however, talk to your health care 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.

The Test Sample

What is being tested?

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 acute and chronic symptoms 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 than normal, and the blood becomes more concentrated.This can cause excessive thirst, frequent urination, dehydration, and – if not enough water is ingested to replace what is being lost – high blood sodium (hypernatremia).

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 (hyponatremia).

The ADH test is not widely used to diagnose these conditions.Often, a diagnosis is made on the basis of clinical history and other laboratory tests, such as urine and blood osmolality and electrolytes.

ADH deficiency is called diabetes insipidus. There are two types of this disorder: central and nephrogenic.

  • 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 the excretion of large quantities of dilute urine.

Increased levels of ADH are often seen with "syndromes of inappropriate antidiuretic hormone" (SIADH) secretion.SIADH is characterized by inappropriate (that is, not due to high blood osmolality or low blood volume) production of too much ADH, resulting in water retention, low blood sodium, and decreased blood osmolality.It 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, excessive ADH causes low blood sodium and osmolality because water is retained and blood volume is increased.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed for an ADH test. However, talk to your health care 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.

The Test

How is it used?

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).

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

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 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:

  • 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.

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.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.

Increased ADH levels are often associated with SIADH, which 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.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.

A low ADH may be seen with central diabetes insipidus, excessive water drinking, and with low serum osmolality. An increased ADH may be seen with nephrogenic diabetes insipidus, with dehydration, trauma, and surgery.

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.

Is there anything else I should know?

In general, the ability to concentrate urine decreases with age.

ADH secretion increases when a person is standing, at night, and with pain, stress and exercise.Secretion decreases with hypertension and when someone is lying down.

Many drugs 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.