Endocrine Abstracts

Background: Transsphenoidal surgery (TSS) for pituitary disease can impair hypothalamic–pituitary–adrenal (HPA) axis function, necessitating peri-operative glucocorticoid replacement. At our centre, serum cortisol is measured seven days post-operation. Patients with values above 350 nmol/l discontinue hydrocortisone and undergo a short Synacthen test (SST) at six weeks to confirm recovery. The value of this confirmatory test is uncertain. We evaluated whether the day-7 cortisol concentration predicts subsequent adrenal sufficiency, aiming to inform a more efficient postoperative pathway.

Methods: A retrospective cohort study was conducted in adults undergoing TSS between July 2021 and July 2024. Adrenal sufficiency was defined as baseline cortisol >225 nmol/l and peak stimulated cortisol >430 nmol/l on six-week SST. Day-7 cortisol was evaluated as a predictor of SST success using receiver operating characteristic (ROC) analysis, with Youden’s J statistic identifying the optimal threshold. Internal validation was performed with 2000 bootstrap replications. Pre-specified thresholds of >300 nmol/l and >350 nmol/l were also assessed.

Results: Ninety-eight patients were included; 45.9% achieved SST-defined adrenal sufficiency. Day-7 cortisol demonstrated excellent discrimination for SST success (AUC 0.862, 95% CI 0.788–0.937). The optimal threshold (328.5 nmol/l) achieved sensitivity 75.6% (61.3–85.8) and specificity 88.7% (77.4–94.7). The >300 nmol/l and >350 nmol/l thresholds yielded sensitivities of 77.8% and 60.0%, and specificities of 81.1% and 90.6%, respectively. Bootstrap validation confirmed robustness (median optimal threshold 325.5 nmol/l, 95% CI 237.5–330.5; AUC 0.866, 0.781–0.930).

Conclusion: A single day-7 serum cortisol measurement accurately predicts recovery of the HPA axis after TSS. A threshold >328 nmol/l provides optimal test performance, while 300 nmol/l and 350 nmol/l cut-offs offer flexibility depending on whether clinical priorities favour sensitivity or specificity. Adoption of a data-informed day 7 cortisol threshold could reduce unnecessary follow-up SSTs.