AVP and neurohypophyseal diabetes insipidus: Comparisons between the group of patients with AVP deficiency 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 (median = 2.5 pmol/L and IQR = 2.0–3.0 pmol/L versus median = 3.9 pmol/L and IQR = 2.9–6.1 pmol/L, p < .01), Day 2 copeptin levels (median = 2.3 pmol/L and IQR = 2.0–2.6 pmol/L versus median = 4.0 pmol/L and IQR = 2.9–6.2 pmol/L, p < .01) and Day 8 copeptin levels (median = 2.0 pmol/L and IQR = 1.6–2.2 pmol/L versus median = 3.7 pmol/L and IQR = 2.6–5.1 pmol/L, p < .01).