Lastly, the presence of hypernatremia (Na > 147 mmol/L) associated with basal copeptin levels ≤ 4.9 pmol/L is indicative of AVP deficiency, whereas unstimulated copeptin levels ≥ 21.4 pmol/L would indicate AVP resistance [136,137,138,139,140]. Here, AVP is linked to neurohypophyseal diabetes insipidus.