Cosyntropin Stimulation Testing is More Selective than Postoperative Day 1 Basal Cortisol for Diagnosing Secondary Adrenal Insufficiency After Unilateral Adrenalectomy

Background Secondary adrenal insufficiency (SAI) may occur in patients after unilateral adrenalectomy for adrenal-dependent hypercortisolism (HC) or primary aldosteronism (PA). This study aimed to assess whether postoperative day (POD) 1 basal cortisol was predictive of an abnormal cosyntropin stimulation test (CST) result and the need for glucocorticoid replacement (GR). Methods A retrospective review of consecutive patients who underwent unilateral adrenalectomy for HC, PA, or both between September 2014 and September 2022 was performed. On POD1, CST was performed for all the patients with HC, and before 2021 for all the patients with PA. The patients with an abnormal CST result were deemed at risk of SAI and discharged with GR. Receiver operating characteristic (ROC) curves were generated to evaluate the sensitivity (SN) and specificity (SP) of basal cortisol thresholds to predict an abnormal CST result. Results The patients underwent unilateral adrenalectomy for overt hypercortisolism (OH; n = 42), mild autonomous cortisol excess (MACE; n = 70), mixed PA/HC ( n = 22), or PA ( n = 73). On POD1, CST was performed for 152 patients (93% OH, 96% MACE,73% PA/HC, 41% PA), and 80 patients (53%) had SAI (67% OH, 55% MACE, 44% PA/HC, 33% PA). The SN and SP of a basal cortisol level of 10 µg/dL or lower to predict an abnormal CST were respectively 92% and 77% for OH, 94% and 73% for MACE, 100% and 85% for PA, and 100% and 67% for PA/HC. The optimal basal cortisol level for predicting an abnormal CST for patients with PA or PA/HC was 5 µg/dL or lower (SN/SP, 100%). Conclusions After unilateral adrenalectomy for HC, PA, or mixed PA/HC, POD1 CST improved identification of patients at risk for SAI compared with basal cortisol levels alone. The authors recommend that POD1 CST be performed to determine the risk for SAI and the need for postoperative GR after unilateral adrenalectomy for patients with HC.