From the Guidelines
The Short Synacthen Test (SST) is a diagnostic procedure used to assess adrenal gland function by measuring the body's cortisol response to synthetic ACTH (adrenocorticotropic hormone), primarily used to diagnose adrenal insufficiency, including primary and secondary adrenal insufficiency. The test involves administering 250 micrograms of synthetic ACTH (tetracosactide/Synacthen) either intramuscularly or intravenously, with baseline and additional blood samples taken at 30 minutes and 60 minutes after administration to measure cortisol response 1.
Key Points:
- A normal response shows cortisol levels rising to above 500-550 nmol/L (18-20 μg/dL) at either time point.
- The test works because synthetic ACTH mimics the natural hormone that stimulates the adrenal cortex to produce cortisol.
- In healthy individuals, this stimulation causes a significant rise in cortisol levels, while those with adrenal insufficiency show a blunted or absent response.
- The SST is preferred over longer tests because it's quicker, more convenient, and provides reliable diagnostic information in most cases.
- Patients should discontinue corticosteroid medications before testing when possible, as these can interfere with results, as suggested by guidelines for the diagnosis and management of primary adrenal insufficiency 1.
Diagnosis and Management:
- The diagnosis of primary adrenal insufficiency (PAI) should be considered in all patients presenting with unexplained collapse, hypotension, vomiting, or diarrhea, and the diagnostic test for primary PAI should be paired measurement of serum cortisol and plasma ACTH 1.
- The SST is a useful diagnostic tool in this context, with a peak serum cortisol <500 nmol L1 being diagnostic of PAI in equivocal cases 1.
- Treatment of suspected acute adrenal insufficiency should never be delayed by diagnostic procedures, and patients with PAI should be reviewed at least annually, with assessment of health and well-being, measurement of weight, blood pressure, and serum electrolytes 1.
From the Research
Purpose of the Short Synacthen Test
The Short Synacthen test, also known as the Adrenocorticotropic hormone (ACTH) stimulation test, is used to assess adrenal reserve and diagnose adrenal insufficiency 2, 3, 4, 5, 6.
Key Objectives
- The main objective of the Short Synacthen test is to evaluate the adrenal gland's response to ACTH stimulation 2.
- The test helps to diagnose primary or secondary adrenal insufficiency by measuring cortisol levels after ACTH administration 3, 6.
Test Procedure
- The test involves administering a synthetic form of ACTH, such as Synacthen, intravenously or intramuscularly 2, 5, 6.
- Blood samples are collected at baseline and at 30 and 60 minutes after ACTH administration to measure cortisol levels 2, 5.
- Salivary glucocorticoids can also be measured as a non-invasive alternative to blood sampling 4.
Interpretation of Results
- A peak plasma cortisol level of 420 nmol/L or higher at any time point is considered adequate to rule out adrenal insufficiency 2.
- A cortisol level of less than 18.0 microg/dl at 60 minutes after ACTH administration is indicative of adrenal insufficiency 6.
- The test results can help identify patients with primary or secondary adrenal insufficiency and guide treatment decisions 3, 6.
Advantages and Limitations
- The Short Synacthen test is a widely used and reliable diagnostic tool for adrenal insufficiency 2, 3.
- However, the test may have limitations, such as the need for venous cannulation and blood sampling, which can be invasive and resource-intensive 4.
- Non-invasive alternatives, such as salivary glucocorticoid measurement, are being developed to simplify the test procedure 4.