Can a random serum cortisol reduce the need for short synacthen tests in acute medical admissions?

BACKGROUND: Short synacthen tests (SSTs) are frequently performed in medical inpatients with suspected adrenocortical insufficiency. The utility of a random or baseline serum cortisol in this setting is unclear. We determined random cortisol thresholds that safely preclude SSTs in acute medical admissions. METHODS: We analysed SSTs in acute non-critically ill general medical patients (n = 166, median age 66, range 15-94 y; men 48%, women 52%). The SST was defined according to the 30-min cortisol as 'pass' (>550 nmol/L) or 'fail' (< or =550 nmol/L). Receiver operating characteristics (ROC) curves were generated to determine the predictive value of the basal cortisol for a failed SST. RESULTS: Of 166 SSTs, a pass was seen in 127 (76.5%) tests, while 39 (23.5%) tests failed the SST. ROC curves showed that no single cut-off point of the baseline cortisol was adequately both sensitive and specific for failing the SST despite a good overall predictive value (area under curve 0.94; 95% confidence interval 0.89-0.98). A basal cortisol <420 nmol/L had 100% sensitivity and 54% specificity for failing the SST, while a basal cortisol <142 nmol/L had 100% specificity and 35% sensitivity. Restricting the SST to patients with a basal cortisol <420 nmol/L would have prevented 44% of SSTs while correctly identifying all patients who failed the SST. CONCLUSION: A baseline serum cortisol may prevent unnecessary SSTs in medical inpatients with suspected adrenocortical insufficiency. However, SSTs are still indicated in patients with random cortisol <420 nmol/L, or where the suspicion of adrenal insufficiency is compelling.