AVP and neurohypophyseal diabetes insipidus: Comparison of copeptin levels between the SIAD group, the AVP deficiency group and the group of patients who did not develop any water or sodium disorders post‐TSS revealed statistically significant differences for Day 1 copeptin levels (p = .01), Day 2 copeptin levels (p = .02) and Day 8 copeptin levels (p < .001) (Figure 1B).