BACKGROUND: The Short Synacthen Test (SST) is used to rule in or out adrenal insufficiency. Failure of stimulation by native ACTH in pituitary or hypothalamic disease can also result in a lack of response to Synacthen, but a normal Synachten test does not absolutely exclude central hypoadrenalism. A morning cortisol ± ACTH level may provide adequate information to avoid the need for a stimulation test.
AIM: To determine the appropriateness of the use of the SST in a single centre.
METHODS: A retrospective audit of all SSTs for one year was conducted. Indications, orderer, availability of a morning cortisol and/or or ACTH and results were recorded.
RESULTS: 27 SSTs were performed in adults. A morning cortisol was available before the SST in 12 patients. In 8 patients, a morning cortisol alone adequately confirmed normal adrenal and in a further 3, central hypodrenalism was not adequately assessed. In 13 patients with borderline morning cortisol levels, the laboratory comment did not consider central hypoadrenalism where the clinical picture might have suggested the same. In total, only 3 tests were regarded as completely appropriate.
DISCUSSION: The SST is commonly used without first measuring the morning cortisol and ACTH. Central hypoadrenalism does not seem to be considered by the order or pathology comment when the morning cortisol is borderline and a ‘normal’ response is demonstrated. Early morning low serum cortisol concentrations <80nmol/L has 100% specificity for detecting adrenal insufficiency.1 A morning serum cortisol concentration greater than 415 nmol/L predicts a normal serum cortisol response to insulin-induced hypoglycaemia.1