Copeptin in Differentiation of Polyuria and Polydipsia

The differential diagnosis of patients with polyuria/ polydipsia is often complex, but important for the therapeutic strategy. Challenging is in particular the clinical differentiation between patients with a partial Diabetes insipidus centralis and patients with primary polydipsia as underlying disease, because both groups are associated with similar urinary osmolalities. The determination of plasma arginine vasopressin is unusual in this context, since measurement of AVP is not reliably. C-terminal ProVasopressin (copeptin) is secreted stoichiometrically with AVP from the neurohypophysis, but has a longer half life in the circulation, and is thus easier to measure. Therefore, the investigators will analyze in that study the diagnostic utility of plasma copeptin in the differential diagnosis of polyuria and polydipsia.