AVP and neurohypophyseal diabetes insipidus: found that 3 months after transsphenoidal pituitary surgery, copeptin values of <1.9 pmol/l with normal serum sodium results were the best cut-off value for permanent AVP deficiency with a diagnostic accuracy of 81.8%; however, a copeptin value of ≥3.5 pmol/l excluded AVP deficiency with a negative predictive value of 100% (16).