In this test, the level of anti-diuretic hormone (ADH) is measured in the blood. This hormone is produced in the hypothalamus while it is stored in the back of the pituitary gland (Hypophysis). The function of this essential hormone in the water sector of the body is to prevent dehydration and to maintain a constant (Osmolarity) salinity in the body. This hormone causes the water to be absorbed in the distal convoluted tubule in the kidneys, reducing urine volume. The high concentration of salts and proteins in the blood increases the secretion of hormone, leading to increased water storage in the body and lower concentration of these molecules in the blood. When excessive concentration of these molecules in the blood (low osmolality) decreases the secretion of hormone, increase the volume of urine and remove excess fluid.
When there is no connection between the concentration of these molecules and the amount of hormone released, it can cause excessive storage of water and decrease in the amount of molecules - especially in the amount of sodium in the blood. The level of the hormone is rarely checked in daily life. Quantities are estimated in the blood, depending on the changes in sodium concentration in the blood and urine and from the blood and urine test.