Antidiuretic hormone (ADH) is a hormone that helps your kidneys manage the amount of water in your body. The ADH test measures how much ADH is in your blood. This test is often combined with other tests to find out what is causing too much or too little of this hormone to be present in the blood.
ADH is also called arginine vasopressin. It’s a hormone made by the hypothalamus in the brain and stored in the posterior pituitary gland. It tells your kidneys how much water to conserve.
ADH constantly regulates and balances the amount of water in your blood. Higher water concentration increases the volume and pressure of your blood. Osmotic sensors and baroreceptors work with ADH to maintain water metabolism.
Osmotic sensors in the hypothalamus react to the concentration of particles in your blood. These particles include molecules of sodium, potassium, chloride, and carbon dioxide. When particle concentration is not balanced, or blood pressure is too low, these sensors and baroreceptors tell your kidneys to store or release water to maintain a healthy range of these substances. They also regulate your body’s sense of thirst.
ADH levels that are too low or too high can be caused by a number of different problems.
Too little ADH in your blood may be caused by compulsive water drinking or low blood serum osmolality, which is the concentration of particles in your blood.
A rare water metabolism disorder called central diabetes insipidus is sometimes the cause of ADH deficiency. Central diabetes insipidus is marked by a decrease in either the production of ADH by your hypothalamus or the release of ADH from your pituitary gland.
Common symptoms include excessive urination, which is called polyuria, followed by extreme thirst, which is called polydipsia.
Patients with central diabetes insipidus are often extremely tired because their sleep is frequently interrupted by the need to urinate. Their urine is clear, odorless, and has an abnormally low concentration of particles.
Central diabetes insipidus can lead to severe dehydration if it’s left untreated. Your body won’t have enough water to function.
This disorder is not related to the more common diabetes mellitus, which affects the level of the hormone insulin in your blood.
When there’s too much ADH in your blood, syndrome of inappropriate ADH (SIADH) may be the cause. If the condition is acute, you may have a headache, nausea, or vomiting. In severe cases, coma and convulsions can occur.
Increased ADH is associated with:
- lung cancer
- pancreatic cancer
- bladder cancer
- brain cancer
- systemic cancers that produce ADH
- Guillain-Barrè syndrome
- multiple sclerosis
- acute intermittent porphyria, which is a genetic disorder that affects your production of heme, which is an important part of blood
- cystic fibrosis
Dehydration, brain trauma, and surgery can also cause excess ADH.
Nephrogenic diabetes insipidus is another very rare disorder that may affect ADH levels. If you have this condition, there’s enough ADH in your blood, but your kidney can’t respond to it, resulting in very dilute urine. The signs and symptoms are similar to central diabetes insipidus. They include excessive urination, which is called polyuria, followed by extreme thirst, which is called polydipsia. Testing for this disorder will likely reveal normal or high AHD levels, which will help distinguish it from central diabetes insipidus.
Nephrogenic diabetes insipidus is not related to the more common diabetes mellitus, which affects the level of insulin hormone in the blood.
A healthcare provider will draw blood from your vein, usually on the underside of the elbow. During this process, the following occurs:
- The site is first cleaned with an antiseptic to kill germs.
- An elastic band is wrapped around your arm above the vein. This causes the vein to swell with blood.
- Your healthcare provider gently inserts a needle syringe into your vein. Blood collects in the syringe tube. When the tube is full, the needle is then removed.
- The elastic band is then released, and the needle puncture site is covered with sterile gauze to stop the bleeding.
Many medications and other substances can affect the levels of ADH in your blood. Before the test, your doctor may ask you to avoid:
The uncommon risks of blood tests are:
- excessive bleeding
- blood pooling under the skin called a hematoma
- infection at the puncture site
Abnormally high levels of ADH may mean you have:
- a brain injury or trauma
- a brain tumor
- a brain infection
- a central nervous system infection or tumor
- a lung infection
- small cell carcinoma lung cancer
- fluid imbalance after surgery
- syndrome of inappropriate ADH (SIADH)
- a stroke
- nephrogenic diabetes insipidus, which is very rare
- acute porphyria, which is very rare
Abnormally low levels of ADH may mean:
- pituitary damage
- primary polydipsia
- central diabetes insipidus, which is rare
An ADH test alone is usually not enough to make a diagnosis. Your doctor will probably need to perform a combination of tests. Some tests that may be performed with an ADH test include the following:
- An osmolality test is a blood or urine test that measures the concentration of dissolved particles in your blood serum and urine.
- An electrolyte screening is a blood test that’s used to measure the amount of electrolytes, usually sodium or potassium, in your body. It’s also used to measure the pH, or acidity, of your blood.
- A water deprivation test examines how frequently you urinate if you stop drinking water for several hours.