Because of its very low concentration in blood, at picomolar levels, and its instability after collection, ADH is not routinely measured in most clinical laboratories. The menu of offerings on commercial automated immunoassay systems that employ chemiluminescence (CIA) principles do not include ADH.
Immunoassays that use radioisotopes are primarily used for ADH determination, and the number of laboratories with a gamma counter is decreasing. Some laboratory-developed methods that employ chromatographic principles have been used to measure ADH.
Urine osmolality is often used in a reflexive capacity as an indication of the need for ADH determination. If urine osmolality remains very low, with large amounts of dilute urine being produced even in challenges of water deprivation, ADH is subsequently measured to detect a diminished degree of production.
