As of Monday, March 4th, 2019, due to change at our referral testing facility, testing for ADH/ Vasopressin is no longer available. It has been replaced by copeptin, a more reliable surrogate marker. ADH and copeptin are released in the body in a 1:1 ratio as 2 parts of the arginine vasopressin precursor. Measurement of ADH is difficult in part because of its short half-life. Copeptin is more stable and can be measured by immunoassay. It can therefore be reliably used as a surrogate marker for ADH.