From the Guidelines
The ACTH stimulation test consists of measuring cortisol levels before and after administering synthetic ACTH (cosyntropin) to evaluate adrenal gland function, typically involving a baseline blood sample, an injection of 250 micrograms of cosyntropin, and additional blood samples at 30 and 60 minutes to measure cortisol response. The test is used to diagnose adrenal insufficiency, including primary and secondary adrenal insufficiency, and patients should avoid taking glucocorticoids before the test if possible, as they can interfere with results 1.
Key Components of the Test
- Baseline blood sample to measure cortisol levels
- Injection of 250 micrograms of cosyntropin (Synacthen or Cortrosyn) either intravenously or intramuscularly
- Additional blood samples collected at 30 and 60 minutes after the injection to measure cortisol response
- Normal response: cortisol levels rise significantly above baseline (typically to >18-20 μg/dL or >500 nmol/L), indicating proper adrenal function
Important Considerations
- The test works by mimicking the body's natural stress response, where ACTH from the pituitary stimulates the adrenal cortex to produce cortisol
- A diminished cortisol response suggests impaired adrenal function that requires further investigation and potential treatment
- The high-dose (250-μg) ACTH stimulation test is considered superior to other existing diagnostic tests for primary adrenal insufficiency, with peak cortisol levels below 18 μg/dl indicating adrenal insufficiency 1
- The task force suggested using the high-dose rather than the low-dose ACTH test for the diagnosis of CIRCI due to easier practical modalities and comparable accuracy 1
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Overview of the Adrenocorticotropic Hormone (ACTH) Stimulation Test
The ACTH stimulation test is used to evaluate adrenal function and diagnose adrenal insufficiency. The test involves administering synthetic ACTH, also known as cosyntropin, to stimulate the adrenal glands to produce cortisol.
Components of the ACTH Stimulation Test
- The test typically involves administering a dose of synthetic ACTH, which can range from 1 microg to 250 microg, depending on the specific protocol being used 2, 3, 4.
- Blood samples are collected before and after administration of the ACTH to measure cortisol levels 2, 3, 5, 6, 4.
- The test can be performed using different routes of administration, including intravenous and intramuscular injection 3, 4.
Interpretation of Test Results
- A cortisol level below a certain threshold, such as 18 μg/dL or 500 nmol/L, after 30 or 60 minutes indicates impaired adrenocortical reserve 2, 3, 5, 6.
- Newer specific cortisol assays may have lower thresholds for a normal response, such as 14-15 μg/dL 5.
- Basal cortisol levels can also be used to diagnose adrenal insufficiency, but may have poor sensitivity compared to ACTH-stimulated cortisol levels 3.
Special Considerations
- The test may not be suitable for patients with recent pituitary injury or those receiving high-dose glucocorticoid therapy 2, 6.
- The effective time frame for the test may be limited in patients receiving high-dose glucocorticoid therapy, with some studies suggesting that the test may be used within the first 3 days after initiation of therapy 6.