(kō-pep′tin)
The C-terminal portion of the arginine vasopressin precursor peptide. It is a marker for the release of arginine vasopressin by the hypothalamus during any of several stressful illnesses, including the stress of myocardial infarction, serious infection, or cerebrovascular accident. Assays for copeptin can be used to distinguish diabetes insipidus from water intoxication (primary polydipsia).