Determining the utility of the 60 min cortisol measurement in the short synacthen test

Objective Despite the widespread use of the short synacthen test (SST), there remains no clear consensus on sampling times for the measurement of serum cortisol that best determines adrenal reserve. We set out to establish whether there is any value in measuring serum cortisol at 60min following administration of synacthen. Design Retrospective data analysis of 500 SST results measuring 0, 30 and 60min cortisol levels after administration of 250g of synacthen at 2 large urban National Health Teaching Hospitals in the UK. Patients and measurements Individuals thought to have primary or secondary adrenal insufficiency given 250g of synacthen. Measurements Serum cortisol levels measured at 0, 30 and 60min, looking to see how many people who had adrenal insufficiency at the 30min sample but in whom the 60min sample showed adequate adrenal reserve. Results The results from 384 people were analysed. A total of 276 had normal responses at 30min and also at 60min. A sum of 33 individuals had insufficient' (i.e., <550nmol/l) 30min cortisol levels, rising to550nmol/l at the 60min test. All 75 individuals who were insufficient at 60min were also insufficient at 30min. No individuals passed (550nmol/l) at 30min and then failed (<550nmol/l) at 60min. Conclusions These results suggest that a significant proportion of people undergoing a SST may be inappropriately diagnosed as having adrenal insufficiency if the 60min sample is not measured. We suggest that the 60min sample is measured in all individuals having a SST to prevent unnecessary over-diagnosis of adrenal insufficiency.