Copeptin (Not Only) in Water and Sodium Disorders.

Arginine vasopressin (AVP) is a key regulator of fluid balance and vascular tone. Its diagnostic utility in various disorders is limited by its short half-life, pulsatile secretion, and preanalytical instability. Copeptin, the C-terminal fragment of preprovasopressin, is secreted in equimolar amounts with AVP and offers a stable, easily measurable surrogate marker. This review highlights the clinical relevance of copeptin in the differential diagnosis of polyuria-polydipsia syndrome, hyponatraemia, critical illness, cardiovascular disease and diabetes mellitus. Copeptin improves diagnostic accuracy, particularly in differentiating types of diabetes insipidus and in the early exclusion of acute myocardial infarction. It also shows prognostic value in heart failure, stroke, and diabetic complications. Given its broad diagnostic potential and analytical advantages, copeptin represents a valuable biomarker for AVP-related pathologies.