Basal serum cortisol levels predict a normal response to the Synacthen stimulation test in hospitalised patients

Abstract

Background The short Synacthen test (SST) is widely used to assess the hypothalamus−pituitary−adrenal axis in the outpatient setting. However, in the inpatient setting, technical difficulties to adhere to the protocol may pose a challenge for using this test. Aims To find the most suitable basal serum cortisol (BSC) cut‐off for predicting an adequate response to the SST in non‐critically inpatients without conducting the actual test. Methods Information was retrieved retrospectively from medical files of 197 patients who had had a 250 μg SST between the years 2000 and 2016 at the Shaare Zedek Medical Center. BSC, electrolytes, creatinine, thyroid‐stimulating hormone, blood counts and blood pressure values were evaluated for a correlation with the results of the SST. Results A BSC cut‐off of 280 nmol/L provides a negative predictive value of 94% for adrenal insufficiency (AI). Using a cut‐off of 380 nmol/L increases the sensitivity to 96% and yields a negative predictive value of 95.8%. Conclusions In this study, we found two suitable BSC cut‐offs for predicting an adequate response to the SST in hospitalised patients. We suggest using the lower cut‐off (280 nmol/L) for patients with a low level of suspicion for AI and using the higher cut‐off (380 nmol/L) for patients with a higher level of suspicion. A BSC above this cut‐off makes the diagnosis of AI very unlikely and precludes the need for a Synacthen test.