Central Diabetes Insipidus (DI) is a condition characterised by insufficient production of arginine vasopressin (AVP) by the posterior pituitary. DI is a common complication observed in patients post-pituitary surgery [1], reportedly 16-34% in the literature [2]. To avoid morbidity and prolongation of hospitalisation, post-operative monitoring is key for timely diagnosis and treatment.
Currently, measuring plasma and urine osmolality alongside fluid balance is the mainstay of investigating DI [3]. However, these methods have low sensitivity (<50%) and specificity [2]. Measuring plasma AVP would provide a more accurate diagnosis but it’s hard to quantify due to its unstable nature. Writing in the JCEM, Winzeler et al. [2] show evidence of a solution to this problem, measuring the biomarker copeptin instead.
Copeptin is a stable and reliable marker of AVP release and is cosecreted with AVP in an equimolar ratio [4]. Hypothalamic stress is a stimulus for AVP, hence copeptin, release [5], and surgery is known to cause hypothalamic stress hormone release [6]. Therefore, Winzeler et al. hypothesised a significant postoperative copeptin increase would be observed in patients with intact pituitary function. They further proposed, in contrast, an absence of this significant copeptin increase may predict DI.
The authors conducted a multicentre observational study of 205 patients undergoing surgery for tumours or lesions near the hypothalamus or pituitary gland. For DI diagnosis, patients had electrolyte, fluid balance and DI symptoms such as polyuria and polydipsia checked daily. If the mandatory criterion hypotonic polyuria was observed, other causes were excluded first. This included steroid-induced osmotic diuresis or excessive perioperative fluid intake. If DI was diagnosed, it was treated with fluids or desmopressin. Patients were reassessed at a follow-up appointment at 3 months to determine if DI was permanent. The authors then divided the cohort into two subgroups: DI or non-DI.
The primary outcome of the study was comparing postoperative copeptin levels with development of DI [2]. They measured copeptin values perioperatively and daily afterwards until discharge. A group whose copeptin levels were measured within 12 hours post-surgery were also specifically analysed. This was to capture the surgical stress-induced copeptin peak occurring shortly post-extubation [7], as copeptin decreases significantly the day after surgery [4].