The Anti-diuretic hormone (ADH) test helps to detect cause of antidiuretic hormone deficiencies and excesses. Since the diagnoses of these conditions are often based on clinical history and other laboratory tests (such as blood and urine osmolality, electrolytes), the ADH test alone is not widely in use. Anti-diuretic hormone is produced by the hypothalamus in the brain and stored in the posterior pituitary gland at the base of the brain. ADH helps in regulating water balance in the body. ADH deficiency is often seen with one of two types of diabetes insipidus (Central diabetes insipidus and nephrogenic diabetes insipidus). Excretion of large quantities of dilute urine is seen in both types of diabetes insipidus.