Introduction
The ACTH stimulation test checks whether the adrenal glands can produce enough cortisol after synthetic ACTH is given. It is used when adrenal insufficiency is suspected.
This is a timed, dynamic test requiring blood samples at set intervals. You cannot judge adrenal function from a single random cortisol at home.
Why this test is done
ACTH Stimulation Test is commonly considered in situations such as:
- Suspected Addison disease or secondary adrenal insufficiency
- Checking adrenal recovery after long-term steroid use is reduced
- Unexplained weakness, weight loss, low sodium, or shock
- Clarifying unclear results from other cortisol tests
- Monitoring in some pituitary or adrenal disorders
How the test is done
- A baseline blood sample for cortisol is taken first.
- Synthetic ACTH is given by injection (cosyntropin is common).
- Repeat blood samples are drawn at set times (for example 30 and 60 minutes).
- Some protocols also measure ACTH hormone—centers differ.
Preparation and precautions
- Get exact timing and fasting instructions from the testing center.
- Report steroids, estrogen, and other hormones—they may need adjustment beforehand.
- Severe illness or shock may postpone the test.
- Tell staff about pregnancy or drug allergies.
Understanding results
Your clinician interprets lab or imaging ranges together with your symptoms. Online “normal values” do not always apply to your case.
- If cortisol does not rise adequately, adrenal response may be reduced.
- Cutoff values differ by assay and lab—internet numbers may not apply.
- False normal or abnormal results are possible; clinical context is essential.
- An endocrinologist or your ordering doctor should interpret results; do not start or stop steroids on your own.
Risks or limitations
- Discomfort from injection and repeated blood draws.
- Rare allergy, flushing, or nausea from the injection.
- Samples taken at wrong times can give misleading results.
After the test
- Rest and drink fluids as instructed.
- Follow up with your specialist when the report is ready.
- Seek emergency care for severe weakness, vomiting, or signs of low blood pressure—do not wait for results.
Frequently asked questions
Is a morning random cortisol enough?
It may give an initial clue, but stimulation testing is often needed when adrenal insufficiency is suspected.
Can I take steroids before the test?
Many steroids affect results. Only change medicines on medical advice.
Is this test a treatment?
No. It is diagnostic. Treatment is a separate decision.
Important caution
This article is general health information. It is not personal medical advice or a prescription.
Your clinician decides whether you need this test, how to prepare, and what the results mean. If you have emergency symptoms, go to hospital without waiting for a lab report.