Aims: The short synacthen test (SST) is considered as the gold standard test to assess the viability of the hypothalamic-pituitary-adrenal axis. This study explores the appropriateness of its clinical use in a district general hospital. Furthermore, it assesses the effectiveness of the alternate use of 9AM cortisol in excluding hypoadrenalism and the cost-effectiveness of sampling both 30 and 60 minutes serum cortisol in SST.
Methods: All 222 SSTs performed between 1/8/2015 and 31/07/2016 were evaluated retrospectively for pre-test probability of hypoadrenalism and timing of the test. Based on previous validation studies, a 9AM cortisol of >400 nmol/L and 30-min SST cut-off of >550 nmol/L (Roche-Gen-I assay) was considered indicative of adrenocortical sufficiency. Statistical correlations were obtained between various cortisol indices.
Results: Overall, 12% (n=27) of SSTs were positive; 4% (n=5) in low and 21% (n=22) in high probability patients. Highly significant correlations between 0, 30 and 60min cortisols were observed (P<0.001; R2>0.450). Furthermore, the correlation between 9AM cortisol and abnormal SST was highly significant (P=0.005; R20.615)
Discussion: This study showed majority of the SSTs performed could be avoided and replaced with the 9AM cortisol which has good predictive diagnostic utility. It also showed that the three-point SST (using 0, 30, 60 min cortisol) does not confer any added advantage over two-point SST (0 & 30 min cortisol). Implementation of these recommendations could result in annual cost savings of nearly £15000.