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 does not currently include ADH.
Radioimmunoassays (RIAs) are still available for ADH determination, but the number of laboratories willing to deal with radioactive isotope waste is few. It is now common to measure copeptin (also known as copeptin proAVP or copeptin AVP) instead of ADH. Copeptin is a more stable marker than ADH in plasma. Copeptin is a precursor to ADH, and like ADH, levels increase in response to osmotic stimuli and water deprivation.
Urine osmolality can be used as an indication of the need for further ADH testing. 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.
