Context: 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.
Objective: To establish whether there is any value in measuring serum cortisol at 60 minutes following administration of synacthen.
Design and setting: Retrospective data analysis of 500 SST results measuring 0, 30 and 60 minute cortisol levels after administration of 250 µg of synacthen at 2 large urban National Health Teaching Hospitals in the UK.
Patients: Individuals thought to have primary or secondary adrenal insufficiency.
Intervention: Administration of 250 µg of synacthen.
Main outcome Measures: 0, 30 and 60 minute cortisol levels, looking to see how many people who had adrenal insufficiency at the 30 minute sample but in whom the 60 minute sample showed adequate adrenal reserve
Results: The results from 324 people were analysed. In 7% of people at one institution, and in 11% from the other, the 30 minute cortisol level was insufficient (i.e. <550 nmol/L), but had risen to ≥550 nmol/L at the 60 minute test. All individuals who were insufficient at 60 minutes were also insufficient at 30 minutes.
Conclusions: These results suggest that a significant proportion of people undergoing a SST may be inappropriately diagnosed as having adrenal insufficiency if the 60 minute sample is not measured. We suggest that the 60 minute sample is measured in all individuals having a SST to prevent unnecessary over-diagnosis of adrenal insufficiency.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.
Comparisons of responses at 30 minutes and 60 minutes. Pass=cortisol response greater or equal to 550 or else it is fail. *=McNemar’s test for matched pairs.