Antidiuretic Hormone

Vasopressin, arginine vasopressin, ADH

This test measures how much antidiuretic hormone (ADH) is in your blood.

ADH is made by your hypothalamus. ADH keeps the amount of water in your body in balance. Certain conditions can affect the amount of ADH that your body makes. These include hyponatremia, or low sodium levels in your bodily fluids. They also include diabetes insipidus. Symptoms of this condition include urinating often and being very thirsty.

You may have this test if your healthcare provider thinks you have a problem that affects your ADH levels. 

Your healthcare provider may also order other tests, including a water deprivation test. In this test, you stop drinking fluids for several hours. Then your urine and blood are measured to see how many solid particles they have.

Your provider may also order a water loading test. In this test, you drink certain amounts of water. Then your provider measures the water levels in your urine over time.

You might need an MRI to see if there are any problems with the hypothalamus or pituitary gland.

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

Normal ADH levels in adults vary but are usually less than 2.5 pg/mL.

Higher than normal results may mean that you have a condition called syndrome of inappropriate antidiuretic hormone (SIADH). It causes your body to hold onto too much water instead of getting rid of it in your urine. SIADH may be caused by lung tumors, central nervous system tumors, or a fluid problem after surgery. Or you may have porphyria. This is a very rare blood enzyme deficiency.

Low levels of ADH may mean you have diabetes insipidus or damage to the pituitary gland. Or you may have primary polydipsia. This is extreme thirst because of hypothalamus problems or mental illness.

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Taking a blood sample with a needle carries small risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

Rarely smoking can make ADH levels higher. Other uncommon causes of higher levels of ADH are pregnancy and taking morphine or certain antidepressants.   

Tell your healthcare provider if you smoke, drink alcohol, or take medicines.  Be sure your provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.