Arginine vasopressin (AVP), or antidiuretic hormone (ADH), is a nonapeptide produced by the hypothalamus and released from the posterior pituitary in response to extracellular fluid hyperosmolarity and hypovolemia. AVP promotes the concentration of urine by increasing water reabsorption in the kidney tubules.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 isn't 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. An AVP test is a simple blood test that checks the amount of ADH levels in the blood by a method called radioimmunoassay.