Copeptin in the diagnosis and management of renal tubular disorders.

Copeptin, a stable glycopeptide derived from the precursor of arginine vasopressin (AVP), has emerged as a valuable surrogate biomarker for AVP due to its stability and ease of measurement. This narrative review explores the physiological role of copeptin, its utility as a diagnostic and prognostic biomarker in different kidney diseases, and its clinical relevance in renal tubular disorders. The clinical application of copeptin as a diagnostic biomarker is best established in the differential diagnosis of polyuria-polydipsia syndrome (PPS), distinguishing nephrogenic diabetes insipidus (NDI) from central diabetes insipidus (CDI) and primary polydipsia (PP). Baseline and stimulated copeptin levels demonstrate high diagnostic accuracy, although methodological and population-specific limitations exist, especially in pediatrics. Copeptin has also proved to be a marker of disease severity in a wide range of acute pathologies. In chronic kidney disease (CKD), it correlates negatively with kidney function, and it has been shown to be a marker of kidney function decline in kidney transplant patients and in autosomal dominant polycystic kidney disease (ADPKD). Regarding renal tubular disorders, CKD has increasingly been recognized in these patients, potentially driven by persistent volume depletion and activation of the renin-angiotensin-aldosterone system. Copeptin may offer an objective assessment of volume status and disease severity, particularly in infants and young children. However, further studies are needed to define standardized reference values, clarify its mechanistic role, and validate its prognostic utility in tubulopathies. Copeptin holds potential as both a diagnostic and prognostic biomarker in renal tubular disease, with implications for clinical practice and patient management.