ACTH (Cosyntropin) Stimulation Test – Adrenal Function and Cortisol Response
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What Is the Adrenocorticotropic Hormone (Cosyntropin) Stimulation Test?
The Adrenocorticotropic Hormone (ACTH) Stimulation Test—also known as the Cosyntropin Stimulation Test—is a diagnostic blood test used to evaluate how well your adrenal glands are functioning. Specifically, it measures your body’s ability to produce cortisol, a vital hormone that helps regulate blood pressure, blood sugar, metabolism, and your body’s response to stress.
Why Is the Cosyntropin Stimulation Test Done?
Doctors may order the ACTH stimulation test to:
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Diagnose adrenal insufficiency (such as Addison’s disease)
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Evaluate pituitary gland disorders (secondary adrenal insufficiency)
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Investigate low cortisol levels found on routine lab work
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Monitor adrenal gland function in people using long-term corticosteroids
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Assess unexplained symptoms like fatigue, weakness, low blood pressure, or weight loss
How the Test Works
The test involves measuring your blood cortisol levels at specific times after receiving an injection of Cosyntropin (a synthetic form of ACTH):
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Baseline: A blood sample is taken to measure your initial cortisol level.
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Injection: Cosyntropin is given by intramuscular (IM) or intravenous (IV) injection.
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Follow-up measurements: Blood samples are drawn again at 30 minutes and 60 minutes after the injection.
These timed samples help determine how well your adrenal glands respond to ACTH stimulation.
What Do Normal Results Look Like?
Cortisol reference ranges can vary by laboratory and the specific test used. Typical values are:
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Baseline (pre-injection): 6–18 µg/dL (may vary by lab and time of day)
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30 minutes post-injection: ≥18 µg/dL
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60 minutes post-injection: ≥20 µg/dL
A normal response is an increase in cortisol levels to at least 18–20 µg/dL at either the 30-minute or 60-minute mark. Always interpret results using your laboratory’s reference ranges.
What Abnormal Results May Indicate
| Result Pattern | Possible Interpretation |
|---|---|
| Low baseline + low response | Primary adrenal insufficiency (Addison’s disease) |
| Low baseline + delayed/partial response | Secondary adrenal insufficiency (pituitary dysfunction) |
| Normal baseline + blunted response | Subclinical adrenal suppression (often due to recent corticosteroid use) |
Abnormal or borderline results may require further testing, such as an insulin tolerance test or additional hormone studies, for a definitive diagnosis.
Preparing for the ACTH Stimulation Test
To ensure accurate results:
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Follow your doctor’s instructions about medications, especially corticosteroids or hormone therapies.
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Fast or avoid strenuous activity, if advised.
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Inform your healthcare provider about any recent illness or long-term medication use.
Are There Any Risks?
The ACTH stimulation test is generally safe. Rarely, you may experience mild discomfort at the injection site, lightheadedness, or temporary changes in blood pressure.
Takeaway
The ACTH (Cosyntropin) Stimulation Test is a reliable and widely used tool for evaluating adrenal gland health. It helps detect conditions like Addison’s disease or pituitary-related hormone imbalances, guiding appropriate treatment and long-term care. If you're experiencing unexplained fatigue, low cortisol levels, or suspect adrenal issues, this test can provide essential answers. Always discuss your results and next steps with your healthcare provider.
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Biomarkers included in this panel:
Adrenocorticotropic Hormone (ACTH) is a critical hormone produced by the pituitary gland in the brain. Its main job is to signal your adrenal glands, located on top of the kidneys, to release cortisol — the body’s key stress hormone. A
Learn moreCortisol Baseline (pre-injection) refers to the initial cortisol level measured in the blood before administering synthetic ACTH (Cosyntropin) as part of the ACTH stimulation test, which evaluates adrenal gland function. Cortisol is a vital hormone p
Learn moreCortisol, 30 minutes post-injection is a key measurement taken during the ACTH (Cosyntropin) Stimulation Test to evaluate how well your adrenal glands respond to stimulation. It reflects the level of cortisol in the blood 30 minutes after an injectio
Learn moreCortisol, 60 minutes post-injection measures the level of cortisol in the blood one hour after an injection of synthetic ACTH (Cosyntropin) during the ACTH stimulation test. This measurement helps evaluate how well the adrenal glands sustain cor
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