Copeptin as a Marker for Vasopressin Dysregulation and Diagnosis

Arginine vasopressin (AVP) is a neuroendocrine hormone essential for fluid balance, vascular tone, and the endocrine stress response. However, its clinical measurement is limited by instability and technical challenges. Copeptin, the C-terminal segment of the AVP precursor, is secreted in equimolar amounts with AVP and serves as a stable, measurable surrogate.

This mini-review outlines the synthesis, release, and physiological roles of AVP and copeptin, emphasizing their relevance in endocrine regulation. It highlights copeptin's diagnostic utility in differentiating AVP-deficiency (AVP-D), AVP-resistance (AVP-R), and primary polydipsia (PP): conditions that share overlapping clinical features. Traditional diagnostic methods such as the water deprivation test (WDT) are contrasted with copeptin-based approaches, which offer improved accuracy and patient tolerability. The review summarizes diagnostic thresholds for baseline and stimulated copeptin levels using stimulation, such as hypertonic saline or arginine, and discusses their integration into clinical algorithms.

Copeptin has emerged as a reliable endocrine biomarker for AVP secretion and is increasingly used in the diagnostic evaluation of polyuria-polydipsia syndromes. Its stability, accessibility, and diagnostic performance support its adoption as a first-line tool in endocrine diagnostics.