At 60 min, a stimulated copeptin of > 5.2 pmol/l provided a specificity of 97% (95% CI [0.92-1.00]) and sensitivity of 69% (95% CI [0.57–0.81]) for diagnosing primary polydipsia, correctly diagnosing 69% (n = 40/58) of patients with primary polydipsia and falsely diagnosing 3% (n = 1/38) patients with AVP deficiency. Here, AVP is linked to neurohypophyseal diabetes insipidus.