MON-155 Retrospective Cross-Sectional Study to Assess the Utility of 30 vs 60 Minutes Serum Cortisol Value Attained During a Short Synacthen Test (SST)

Abstract

Background SST is done to assess adrenal gland function by measuring basal serum cortisol followed by injecting 250 μg of Synacthen (ACTH) & measuring cortisol at 30 & 60 minutes. Design All patients over 14 years (adulthood age in the region) who had undergone a SST from January 2010 to December 2017 were included. Patients who underwent pituitary surgery in preceding 2 months, on exogenous steroids, opioids & oral contraceptives were excluded. Stimulated cortisol of 550 nmol/L or more achieved at 30, 60 minutes or both was classified as a normal response. Results 965 patients were identified from pharmacy, medical & laboratory records. 116 patients were excluded and 849 were included in the analysis. Mean age was 50.5 ± 20.45 years. Mean weight was 67 ± 21 Kg. 54% patients were female. Mean basal, 30 and 60 minutes cortisol values after ACTH injection were 394 ± 286.58 nmol/L, 722 ± 327.11 nmol/L, 827 ± 369.30 nmol/L respectively. 715 patients (84 %) had a normal response and 134 patients (16 %) had suboptimal response. Primary and secondary adrenal insufficiency was diagnosed in 10% and 35% respectively. No ACTH value was available in 55% of the patients. Suboptimal response was observed at 30 minutes in 9.49% (n=72) of the patients: all crossed 550 nmol/L threshold at 60 minutes. Mean change of cortisol level from baseline to 30 minutes was 240 nmol/L in this particular sub group which was higher than the mean change of 152 nmol/L observed in patients who failed the test overall up to 60 minutes. No patient with optimal response at 30 minutes had suboptimal response at 60 min. Morning basal cortisol threshold of 226 nmol/L or over had 80% sensitivity, 71 % specificity & 93% positive predictive value to detect a normal SST (P-value <.0001). Conclusion 60 minute cortisol correctly identified all normal and abnormal results. Relying only on 30 min value resulted in significant false positive results. Morning basal cortisol over 226 nmol/L should be considered reliable threshold for adequate adrenal function particularly when clinicians have low pretest probability for hypoadrenalism.