Is a 0900-h serum cortisol useful prior to a short Synacthen test in outpatient assessment?

Abstract

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 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 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.