Background: The short synacthen test (SST) is the gold standard investigation for the evaluation of adrenal insufficiency and is also frequently used for the evaluation of the hypothalamic-pituitary-adrenal (HPA) axis. The 0900-h serum cortisol concentration has also been evaluated as an indication of cortisol reserve, and a result > 450 nmol/L is highly suggestive of a normal serum cortisol response to the insulin tolerance test, while no patient with a 0900-h serum cortisol < 100 nmol/L had a sufficient response. The aim of this study was to determine if the number of inappropriate SSTs could be reduced if a 0900-h serum total cortisol was done prior to the dynamic function test.
Method: Two hundred and ten SSTs were performed at 0900 h and the response at 30 min evaluated.
Results: Of the 210 SST, 151 (71%) demonstrated a maximum response at 30 min of serum cortisol > 550 nmol/L. All the patients with a 0900-h serum cortisol > 500 nmol/L had an adequate response ( > 550 nmol/L), while no patient with a 0900-h serum cortisol of < 100 nmol/L had an adequate SST response. Twenty one per cent of patients were shown to have had an unnecessary invasive procedure.
Conclusion: We conclude that the SST is of little added value in patients with a 0900-h serum cortisol of less than 100 nmol/L or more than 500 nmol/L and it should be included in the appropriate protocols for endocrine investigation.