Copeptin reliably differentiates various entities of the polyuria polydipsia syndrome; baseline levels >20 pmol/L without prior fluid deprivation identify patients with nephrogenic diabetes insipidus, whereas levels measured upon osmotic stimulation with hypertonic saline or upon non-osmotic stimulation with arginine differentiate primary polydipsia from central diabetes insipidus.
Plasma arginine-vasopressin (AVP) analysis can help in the differential diagnosis of the polyuria-polydipsia syndrome (PPS), even if such investigation is hampered by technical difficulties, conversely to its surrogate copeptin.
Recently, copeptin, the c-terminal portion of the larger precursor peptide of AVP, has been evaluated in the setting of polyuria-polydipsia syndrome and appears to be a useful candidate biomarker for the differential diagnosis.