Endocrine Abstracts

Introduction: The incidence of the syndrome of inappropriate antidiuresis (SIAD) post pituitary surgery is estimated at 3-20% with the condition potentially leading to significant morbidity and prolonged admission. Copeptin, a surrogate marker for vasopressin activity, has been shown to be a diagnostic tool in the diagnosis of AVP deficiency (formerly known as diabetes insipidus) post pituitary surgery. There is limited data regarding the utility of copeptin in predicting SIAD post pituitary transsphenoidal surgery (TSS). The aim of this study was to evaluate the predictive value of copeptin for SIAD post TSS.

Methods: Retrospective analysis of copeptin measured at day 1, day 2 and day 8 post pituitary surgery where data available in consecutive patients undergoing TSS (November 2017 to October 2022). All patients were fluid restricted to 1.5L post TSS except for patients who developed AVP deficiency. Incidence of post TSS SIAD was noted from the electronic patient records and defined as Na<135 mmol/l with serum osmolality<275 mOsm/kg, urine osmolality>×100 mOsm/kg, urine sodium>×30 mmol/l, normal adrenocortical and thyroid function or replaced postoperatively, in euvolemic patients not on diuretics. Logistic regression and Receiver Operating Characteristic (ROC) curves were performed to investigate the value of copeptin in predicting SIAD.

Results: Post TSS copeptin was measured in 133 patients; mean age 34 years (SD= 17 years); 45% (60/133) female. Sixteen patients (12%) had SIAD within 8 days of surgery. Copeptin results were available in 123, 53 and 89 patients for day 1, day 2 and day 8 post TSS, respectively. Logistic regression for day 1 copeptin to predict SIAD gave odds ratio (OR) of 0.98 (95%CI 0.85-1.14, P=0.82) and an area under ROC curve (AUC) of 0.49; day 2 copeptin OR was 0.96 (95%CI 0.73-1.26, P=0.76) with AUC of 0.57; day 8 copeptin OR was 0.98 (95%CI 0.85-1.12, P=0.73) with AUC of 0.44. Logistic regression for day 1 sodium to predict SIAD revealed OR of 0.81 (95CI% 0.69-0.95, P= 0.01) with AUC of 0.70, which remained unchanged after addition of day 1 copeptin to the day 1 sodium regression model.

Conclusions: Incidence of SIAD in our cohort is comparable to published data. We find that post operative copeptin is not helpful in predicting post TSS SIAD and hence would not recommend its use for this purpose.