The short Synacthen (corticotropin) test can be used to predict recovery of hypothalamo-pituitary-adrenal axis function

Context: The 250-mg short Synacthen (corticotropin) test (SST) is the most commonly used tool to assess hypothalamo-pituitary-adrenal (HPA) axis function. There are many potentially reversible causes of adrenal insufficiency (AI), but no data to guide clinicians as to the frequency of repeat testing or likelihood of HPA axis recovery. Objective: To use the SST results to predict adrenal recovery. Design: A retrospective analysis of 1912 SSTs data. Patients: Seven hundred seventy-six patients with reversible causes of AI were identified who had at least two SSTs performed. A subgroup analysis was performed on individuals previously treated with suppressive doses of glucocorticoids (n = 110). Main Outcome Measures: Recovery of HPA axis function. Results: SST 30-minute cortisol levels above or below 350 nmol/L (12.7 μg/dL) best predicted HPA axis recovery [area under the curve (AUC) receiver operating curve (ROC) = 0.85; median recovery time: 334 vs 1368 days, P = 8.5 × 10 -13 ]: 99% of patients with a 30-minute cortisol >350 nmol/L recovered adrenal function within 4 years, compared with 49% in those with cortisol levels < 350 nmol/L. In the subgroup analysis, delta cortisol (30-minute-basal) best predicted the recovery (AUC ROC = 0.77; median recovery time: 262 vs 974 days, P = 7.0 × 10 -6 ). No patient with a delta cortisol <100 nmol (3.6 μg/dL) and a subsequent 1-year random cortisol <200 nmol/L (7.3 μg/dL) recovered HPA axis function. Conclusions: Cortisol levels across an SST can be used to predict recovery of AI and may guide the frequency of repeat testing and inform both clinicians and patients as to the likelihood of restoration of HPA axis function.